SUMMARY

Harderian gland removal caused enlargement of the uteri of adult female albino rats which were maintained in 14 h light and 10 h darkness/day. Constant light exposure led to regression of the ovaries, adrenal glands and Harderian glands while the uteri exhibited a significant hypertrophic response. None of these changes were affected by surgical removal of the Harderian glands. The eyes and the retinas of albino rats maintained under continuous illumination underwent atrophic changes with the receptor cell elements of the retinas completely disappearing within 9½ weeks.

Constant light obliterated the diurnal rhythm in the pineal enzyme, N-acetyltransferase. Neither the activity of pineal hydroxyindole-O-methyl-transferase nor the activity of pineal N-acetyltransferase were influenced by removal of the Harderian glands.

SOCS (suppressor of cytokine signaling)-3 has recently been shown to be an insulin- and tumor necrosis factor (TNF)-alpha-induced negative regulator of insulin signaling. To further clarify a potential involvement of SOCS-3 in the development of insulin resistance, we measured differentiation-dependent SOCS-3 mRNA expression in 3T3-L1 adipocytes and studied its regulation by various hormones known to impair insulin signaling using quantitative real-time RT-PCR. There was a differentiation-dependent downregulation of SOCS-3 mRNA by 50% over the 9 day adipocyte differentiation course. Interestingly, besides insulin and TNF-alpha, chronic treatment of differentiated 3T3-L1 cells with 10 microM isoproterenol for 16 h stimulated SOCS-3 gene expression by about 3.5-fold. Furthermore, isoproterenol stimulated SOCS-3 mRNA expression in a dose-dependent manner with significant activation detectable at concentrations as low as 10 nM isoproterenol. Moreover, a strong 27- and 47-fold activation of SOCS-3 mRNA expression could be seen after 1 h of isoproterenol and GH treatment respectively. The stimulatory effect of isoproterenol could be almost completely reversed by pretreatment of 3T3-L1 cells with the beta-adrenergic antagonist propranolol. Finally, isoproterenol's action could be mimicked by stimulation of G(S)-proteins with cholera toxin and of adenylyl cyclase with forskolin and dibutyryl cAMP. Taken together, our results demonstrate a differentiation-dependent downregulation of SOCS-3 in adipocytes and suggest that SOCS-3 gene expression is stimulated by beta-adrenergic agents via activation of a G(S)-protein-adenylyl cyclase-dependent pathway. As SOCS-3 is a novel inhibitor of insulin signaling, the data support a possible role of this protein as a selectively regulated mediator of catecholamine-induced insulin resistance.

ABSTRACT

A sensitive and specific heterologous radioimmunoassay for FSH-suppressing protein (FSP or follistatin) was applied to ovine plasma. Following a logit–log dose transformation, parallel dose–response lines were observed between purified bovine 35 kDa FSP used as standard and serial dilutions of ewe plasma. Activin-A, inhibin-A and a range of other proteins showed low (<0·5%) cross-reactivity in the assay. Daily variations in the peripheral concentrations of FSP were measured across the ovine oestrous cycle. The peripheral concentrations of plasma FSP in adult ewes revealed a significant (P <0·01) increase (33%) during the luteal phase above follicular phase levels, peaking 10 days after the LH surge. FSP concentrations were determined in arterial and venous plasma from the ovary, head, kidney and liver. A significant (P <0·05) increase across the ovary was detected with no significant differences across the head, liver and kidney.

To investigate the relationship between gonadal FSP and the pituitary, ewes underwent ovariectomy and hypophysectomy. FSP levels rose (100–110%, P <0·01) during the period of surgery for both bilateral ovariectomy and sham ovariectomy, and then decreased significantly (37–44%) at 4–6 h after surgery. A further rise in plasma FSP (180–200% increase above pretreatment levels, P < 0·001) was observed 10–12 h after ovariectomy and sham ovariectomy. FSP levels then returned to preoperative levels during the following 26 h. Plasma FSP levels in long-term ovariectomized and hypophysectomized ewes were not significantly different from preoperative levels.

To determine whether the pattern of plasma FSP seen during the ovariectomy study was due to the effect of the induction of anaesthesia, ewes were treated with sodium thiopentone and halothane or 0·9% (w/v) NaCl by procedures of similar duration to that used during surgery. Both treatments resulted in an elevation of FSP levels (33–62%) over pretreatment values only at the time of induction of anaesthesia. To examine further whether this rise in plasma FSP observed after anaesthesia was due to a stress response and therefore under the control of the pituitary-adrenal axis, ewes were treated with ACTH, dexamethasone or saline only. A further group of sheep were exposed to a barking dog for 10 min. No change in FSP levels compared with pretreatment levels or saline-treated controls were noted following any of these treatments.

It was concluded that (1) FSP is present in the peripheral circulation; (2) ovariectomy contributes to plasma FSP, but no discernible contribution to circulating levels was evident from the head, liver or kidney; (3) plasma FSP levels rose significantly during the luteal phase of the ovine oestrous cycle; and (4) FSP secretion may be associated with a stress response, perhaps related to animal handling and intensive blood sampling through mechanisms that are as yet unclear.

Journal of Endocrinology (1993) 137, 433–443

ABSTRACT

The present study was undertaken to determine (1) whether the rabbit feto-placental unit maintains corpora lutea systematically and/or locally and (2) the interrelationships between conceptus number, luteal weight, luteal progesterone concentrations and serum progesterone levels. Thirty-three does were divided into the following treatment groups: (I) bilaterally pregnant, two ovaries; (II) unilaterally pregnant, two ovaries; (III) bilaterally pregnant, one ovary; (IV) unilaterally pregnant, one ovary, contralateral and (V) unilaterally pregnant, one ovary, ipsilateral. Blood samples were obtained from all rabbits on days 6, 9, 12, 15, 18 and 21 post coitum. Does were killed on day 21, and the percentage of viable fetuses, fetal weights, and luteal weights recorded. Blood samples and corpora lutea were analysed for progesterone.

Serum progesterone levels were similar for all groups until day 9 post coitum. Levels in groups III, IV and V declined significantly between days 9 and 12 following removal of one ovary at day 9. Fetal viability, fetal weights and luteal progesterone concentrations did not differ among any of the groups. Luteal weights did not differ among groups I, III, IV and V, but luteal weights of animals in group II were lower than those of group I (P<0·05). Ratios of viable fetuses to number of corpora lutea ranged from 1:11–10:5. No differences were observed in serum progesterone, luteal weights or luteal progesterone concentrations among animals with two conceptuses and those with seven or more, but serum progesterone levels in does with only one conceptus were lower than those in does with more (P<0·05). These results indicate that the feto-placental unit maintains corpora lutea systemically and that the high rate of pregnancy failure by day 21 in does with only one conceptus is due to the inability of a single conceptus to maintain normal serum progesterone levels even though the corpus luteum weight is not affected.

J. Endocr. (1986) 109, 107–110

Recent studies suggest that high glucose concentrations impair insulin receptor phosphorylation and kinase activation in certain cell models. To examine whether such an effect of glucose can also be demonstrated in vivo, insulin receptor kinase activation was studied in erythrocytes from 11 patients with non-insulin-dependent diabetes (NIDDM), before and after reduction of hyperglycemia (from 14.6+/-1.6 to 6.6+/-0.5 mmol/l fasting plasma glucose within 8.6+/-0.6 days). For the measurement of receptor kinase activation, cells were incubated with insulin (0-400 nmol/l), solubilized and insulin receptors immobilized to microwells coated with anti-insulin receptor antibody. Kinase activity towards insulin receptor substrate-1 and insulin binding were then measured in these wells. Kinase activities (expressed as amol phosphate transferred per min and per fmol insulin binding activity) were similar before (2.4+/-0.4 and 32.2+/-2.0 amol/min per fmol with 0 and 400 nmol/l insulin, respectively) and after improvement of metabolic control (2.4+/-0.5 and 32.0+/-2.3 amol/min per fmol with 0 and 400 nmol/l insulin, respectively). Moreover, activities were also similar in 22 hyperglycemic patients with NIDDM (2.1+/-0.3 and 35.1+/-1.4 amol/min per fmol with 0 and 400 nmol/l insulin, respectively) compared with those in 21 non-diabetic control individuals (2.1+/-0.3 and 34.2+/-1.2 amol/min per fmol with 0 and 400 nmol/l insulin, respectively). We conclude that insulin activation of erythrocyte insulin receptor kinase is not impaired in NIDDM and is not influenced by hyperglycemia.

Tumor necrosis factor (TNF) alpha-induced adipose-related protein (TIARP) has recently been cloned as a TNFalpha-stimulated protein expressed in adipocytes. Its expression is differentiation-dependent and potentially involved in mediating TNFalpha-induced insulin resistance. To further characterize regulation of TIARP gene expression, 3T3-L1 adipocytes were treated with key hormones modulating insulin sensitivity and influencing adipocyte metabolism, and TIARP gene expression was determined by quantitative real-time RT-PCR. Interestingly, TIARP mRNA expression was stimulated almost 9-fold after 500 ng/ml GH were added for 16 h whereas addition of 10 microM isoproterenol, 100 nM insulin and 100 nM dexamethasone for 16 h significantly decreased TIARP gene expression to between 35 and 50% of control levels. In contrast, angiotensin 2 (10 microM) and triiodothyronine (1 microM) did not have any effect. The stimulatory effect of GH was time- and dose-dependent with stimulation occurring as early as 1 h after effector addition and at concentrations as low as 5 ng/ml GH. Moreover, pharmacological inhibition of Janus kinase 2 and p42/44 mitogen-activated protein kinase reversed the stimulatory effect of GH, suggesting that both signaling molecules are involved in activation of TIARP gene expression by GH. Furthermore, an increase of TIARP mRNA could be completely reversed to control levels by withdrawal of GH for 24 h. Taken together, these results show that TIARP is not only responsive to TNFalpha but also to important other hormones influencing glucose homeostasis and adipocyte metabolism. Thus, this factor may play an integrative role in the pathogenesis of insulin resistance and its link to obesity.

Various cytokines, including tumor necrosis factor (TNF) alpha, growth hormone (GH) and interleukin (IL)-6, induce insulin resistance. Recently, it was demonstrated that induction of suppressor of cytokine signaling (SOCS)-3 by TNFalpha and GH is an important mechanism by which these cytokines impair insulin sensitivity. The current study investigated in 3T3-L1 adipocytes whether TNFalpha and GH also upregulate SOCS-1 and SOCS-6, which have both been shown to inhibit insulin signaling potently, and whether IL-6 might alter synthesis of SOCS-1, -3 and -6. Interestingly, 10 ng/ml TNFalpha, 500 ng/ml GH and 30 ng/ml IL-6 induced SOCS-1 mRNA time-dependently with maximal stimulation detectable after 8 h of TNFalpha and 1 h of GH and IL-6 addition respectively. Furthermore, TNFalpha and GH caused sustained upregulation of SOCS-1 for up to 24 h, whereas stimulation by IL-6 was only transient, with SOCS-1 mRNA returning to basal levels 2 h after effector addition. Induction of SOCS-1 was dose-dependent, and significant stimulation was detectable at concentrations as low as 3 ng/ml TNFalpha, 50 ng/ml GH and 10 ng/ml IL-6. Furthermore, stimulation experiments and studies using pharmacologic inhibitors suggested that the positive effect of TNFalpha, GH and IL-6 on SOCS-1 mRNA is, at least in part, mediated by Janus kinase (Jak) 2. Finally, SOCS-3 expression was dose- and time-dependently induced by IL-6, at least in part via Jak2, but none of the cytokines affected SOCS-6 expression. Taken together, our results show a differential regulation of SOCS mRNA by insulin resistance-inducing hormones, and suggest that SOCS-1, as well as SOCS-3, may be an important intracellular mediator of insulin resistance in fat cells and a potential pharmacologic target for the treatment of impaired insulin sensitivity.

Abstract

The aims of this study were to determine the plasma concentrations of follistatin in rams and to assess if the testis contributes to circulating follistatin and if there is uptake or production of follistatin by the head in rams. Catheters were inserted in the carotid artery, jugular vein and spermatic vein of intact rams during the non-breeding season (experiment 1; n=5) and breeding season (experiment 2; n=4). In experiment 1, blood samples were collected from 5 rams every 10 min for 4 h, commencing 20–60 min after surgery. After 2 h of sampling 1 μg gonadotrophin-releasing hormone (GnRH) was injected intravenously. In experiment 2, blood samples were collected from 4 of the rams used in experiment 1 by venipuncture 30 and 15 min before surgery and every 15 min throughout surgery. Commencing 1 h after surgery, matched samples were taken from each of the vessels every 10 min for 4 h (1–4 h after surgery), then every hour for 20 h (4–24 h after surgery) and then every 10 min for 4 h (24–28 h after surgery). In both experiments, follistatin secretion was non-pulsatile and there were no significant differences between the concentrations of follistatin in any of the vessels. There was a significant (P<0·05) increase in the concentrations of follistatin in each of the vessels throughout the 4 h of 10-min sampling in both experiments. In experiment 2 plasma concentrations of follistatin in the jugular vein were significantly (P<0·05) lower before surgery than at other stages of the experiment. During the non-breeding season (experiment 1) the concentrations of follistatin in all vessels were about 2-fold higher (P<0·001) than during the breeding season (experiment 2). Concentrations of follistatin were measured in the testicular tissue of the ram, bull, monkey and rat and were found to be 13·6, 2·1, 2·5, 0·8 ng/g testis respectively. In experiment 3, blood samples were collected every 15 min for 4 h from castrated rams (n=6) in the absence of treatment with testosterone propionate (TP) and after 7 days of treatment with a physiological dose of TP during the breeding and non-breeding seasons. There was no effect of stage of breeding season or TP on the plasma concentrations of follistatin and these concentrations in the castrated rams were similar to the concentrations in the intact rams in experiment 2. In experiment 4, the function of Leydig cells was stimulated by administration of human chorionic gonadotrophin but this had no effect on plasma concentrations of follistatin.

These experiments show that the concentrations of follistatin in the plasma of rams are measurable, that the testis is not the major contributor to circulating follistatin and that there is no significant uptake or production of follistatin by the head in rams. It appears that the contribution of the testis to circulating follistatin may vary with the stage of the breeding season, being greater during the non-breeding season than the breeding season. The gonadotrophins and testosterone do not appear to have a direct effect on the secretion of follistatin in rams. The increase in concentrations of circulating follistatin during surgery and more frequent blood sampling suggest a stress-related effect on the production of follistatin.

Journal of Endocrinology (1996) 149, 55–63

Abstract

Plasma follistatin (FS) concentrations were determined after castration (n=5) or sham castration (n=4) of mature rams. Both treatments resulted in a prolonged increase in FS between 7 and 19 h after surgery, which returned to pretreatment concentrations by 24 h. Tumour necrosis factor-α (TNF-α), a sensitive marker of an acute-phase response, was undetectable in plasma, indicating that the FS response was not induced by trauma due to surgery. In a second experiment, injection of castrated rams (n=4) with ovine recombinant interleukin-1β, an acute-phase mediator, resulted in a sustained rise in FS concentrations within 4 h of injection. Plasma TNF-α concentrations increased transiently within 1 h of interleukin-1β injection, indicating that an acute-phase response had been initiated. Plasma follicle-stimulating hormone (FSH) concentrations were significantly decreased at 8 and 24 h after interleukin-1β injection, strongly suggestive of an inhibitory effect of increased FS concentrations on the secretion of FSH. Injection of castrated rams (n=2) with a control preparation of recombinant interleukin-2 did not induce an acute-phase response, and plasma FS and FSH concentrations were unaffected. These data show that the testis is not a major source of circulating FS, that the increase in circulating FS following sham castration/castration is not due to an acute-phase response, but that conversely FS concentrations are modulated by the acute-phase mediator, interleukin-1β.

Journal of Endocrinology (1996) 151, 119–124

Parathyroid hormone (PTH) stimulates bone resorption as well as bone formation in vivo and in organ culture. The catabolic actions of PTH have been recognized in patients with hyperparathyroidism, or with acute infusion of the N-terminal 1–34 fragment of human PTH (hPTH1–34). Whereas the anabolic actions of daily injection with PTH have been well studied in both humans and mice, the catabolic actions of PTH on murine bone remain to be defined. To do this we sought to create a model with short-term, sustained hyperparathyroidism using osmotic infusion pumps. We treated 10-week-old female C57BL/J6 mice with continuous infusion of hPTH1–34 (8.1 pmol/0.25 μl per h, equivalent to 40 μg/kg per day) or vehicle for 2 weeks, using Alzet osmotic pumps. Bone mineral density (BMD), serum total calcium, hPTH1–34, mouse intact PTH (mPTH1–84), osteocalcin and mouse tartrate-resistant acid phosphatase (mTRAP) activity, and microarchitectural variables of the distal femur were measured. Separately, we compared the effects of intermittent daily injection of hPTH1–34 (40 μg/kg per day) with continuous infusion of hPTH1–34 on BMD and bone markers. Exogenous hPTH1–34 was detected only in the PTH-infused mice. Both intermittent and continuous treatment with hPTH1–34 markedly suppressed endogenous mPTH1–84, but only the latter induced hypercalcemia. Daily PTH injection significantly increased both serum osteocalcin and mTRAP, while continuous PTH infusion showed a strong trend to stimulate mTRAP, with a slight but non-significant increase in osteocalcin. There were significant differences in BMD at all sites between animals treated with the same daily dose of intermittent and continuous hPTH1–34. Microcomputed tomography (μCT) analysis of the distal femurs revealed that hPTH1–34 infusion significantly decreased trabecular connectivity density (P<0.05). Thus, the murine bone response to continuous PTH infusion was quite different from that seen with daily PTH injection. Short-term infusion of hPTH1–34 appears to be a good model to study the mechanisms underlying the catabolic action of PTH in mice.