ABSTRACT

The effects of unilateral section of the right or left vagus nerve (SRVN, SLVN) performed on different days of the oestrous cycle of the rat were analysed. Vagal nerve section on the day of oestrus or on day 1 of dioestrus (D1) altered oestrous cyclicity in a more significant way than when it was performed on day 2 of dioestrus (D2) or pro-oestrus (6/58 maintained normal oestrous cycles compared with 32/39 that did not; P<0.01). Ovulation rate at oestrus was lower in rats with SLVN than in the sham-operated group (32/47 vs 28/32; P < 0.05). The number of ova shed by the left ovary was reduced in sham-operated rats and in animals with SRVN and SLVN, whereas the number shed by the right ovary was not modified. The day of the oestrous cycle on which the vagus nerve was cut also influenced the number of ova shed. No changes in plasma levels of FSH at oestrus were observed in animals with SRVN or SLVN. The results indicate that vagal manipulations performed at the beginning of the oestrous cycle (day of oestrus and D1) induce more changes on oestrous cyclicity and ovulation than when they are performed during the second half of the cycle (D2 and pro-oestrus). In addition, the left ovary is more sensitive to neural manipulation than is the right one.

Journal of Endocrinology (1989) 123, 441-444

We have previously shown that administration of antiprogestin (AP) type II RU486 to ovariectomized (OVX) rats on the morning of pro-oestrus decreases the magnitude of preovulatory gonadotrophin surge. This suggests that the effect of RU486 on LHRH-dependent gonadotrophin release may be independent of its ability to block progesterone actions. The aim of the present research was to study the possible site of RU486 action and to determine whether the gonadotrophin suppressive effect of APs RU486 and ZK299 is dependent on the oestrogen background. Intact or OVX rats in the morning of pro-oestrus were injected s.c. with 4 mg of RU486 or ZK299 (AP type I) at 0900 h on pro-oestrus. At 1830 h, serum concentration of FSH and LH and median eminence (ME) content of LHRH were determined. In the second experiment, the effect of RU486 and ZK299 on pituitary responsiveness to LHRH (100 ng, i.p.) and ME content of LHRH at 1830 h pentobarbital-blocked intact or OVX rats was evaluated. In the last study, the anterior pituitary release of FSH and LH from pro-oestrus or metoestrus donors incubated with or without LHRH (1, 10 or 100 nM) in the presence or absence of APs (20 nM) was evaluated. Both APs reduced serum FSH and LH levels at 1830 h on pro-oestrus in intact and OVX rats. The suppressive effect on gonadotrophin release brought about by AP treatment was also evidenced in PB-blocked intact and OVX rats. This suggested that the inhibitory effect of APs occurred, at least in part, at pituitary level. Furthermore, in the absence of the natural ligand, APs significantly reduced basal and LHRH-stimulated FSH and LH release from pro-oestrous but not from metoestrus pituitaries. In conclusion, these experiments have shown, both 'in vivo' and 'in vitro', that APs RU486 and ZK299 have suppressive effects at pituitary level on basal and LHRH-stimulated FSH and LH secretion, regardless of their antiprogestagenic activity, in pro-oestrus but not in metoestrus.

Diminished GH secretion is a well known association of obesity. As in obese humans, Zucker fatty rats develop a progressive GH deficiency, present at 6 weeks of age and maximal at 10 to 12 weeks. The aim of this study was to investigate the GH dependence of IGF-I gene expression in liver and extrahepatic tissues of the obese Zucker rat as a model of progressive GH reduction during adult life. Six- and 11-week-old obese Zucker rats and their lean littermates were used to compare body weight, glycemia, insulinemia, serum GH and IGF-I levels and IGF-I mRNA expression in liver, heart, aorta, kidney and skeletal muscle. In comparison with lean controls, obese Zucker rats showed at both ages comparable glycemia, severe hyperinsulinemia (mU/ml, mean+/-s.e.m.; 6 weeks 138+/-10 vs 45+/-6 P<0.001; 11 weeks 147+/-14 vs 46+/-3, P<0.001) and lower GH (ng/ml; 6 weeks 1.7+/-0.9 vs 2.7+/-1.1; 11 weeks 1.5+/-0.9 vs 4.2+/-1.2) in the presence of similar circulating IGF-I levels (ng/ml; 6 weeks 774+/-26 vs 694+/-28; 11 weeks 1439+/-182 vs 1516+/-121). Hepatic IGF-I mRNA expression was already reduced at 6 weeks of age due to a significant decrease in the IGF-Ib transcript compared with lean controls (relative units; IGF-Ia: 99+/-2% vs 100+/-5%; IGF-Ib: 69+/-10% vs 100+/-2%, P<0.05) and this reduction was more marked in 11-week-old animals when both IGF-I transcripts were significantly diminished (relative units; IGF-Ia: 80+/-6% vs 100+/-1%, P<0.05; IGF-Ib: 65+/-5% vs 100+/-2%, P<0.01). Extrahepatic tissues expressed almost exclusively the IGF-Ia transcript, the amount of which relative to controls was: (1) similar at 6 weeks and decreased at 11 weeks in kidney and skeletal muscle extracts (relative units; kidney: 6 weeks 88+/-10% vs 100+/-2%; 11 weeks 76+/-3% vs 100+/-4%, P<0.05; vastus lateralis: 6 weeks 95+/-7% vs 100+/-10%; 11 weeks 59+/-4% vs 100+/-2%, P<0.001); (2) similar at both ages in thoracic aorta (relative units; 6 weeks 121+/-6% vs 105+/-5%; 11 weeks: 91+/-14% vs 100+/-4%); and (3) increased at both ages in left ventricle extracts (relative units; 6 weeks 114+/-2% vs 99+/-9%, P<0. 05; 11 weeks 119+/-7% vs 95+/-3%, P<0.05). -specific dependence of IGF-I mRNA on GH levels during adulthood, reflected by the different behavior of IGF-I expression for each tissue in conditions of progressive decrease of GH levels.

Abstract

Pancreastatin is a regulatory peptide known to inhibit insulin secretion and insulin action with a glycogenolytic effect in the liver. This peptide is present in and secreted by many endocrine and chromaffin cells. Abnormalities of glucose, insulin and lipoprotein metabolism are common in patients with hypertension, as well as their first-degree relatives. We have recently studied a group of non-obese hypertensive subjects in which pancreastatin-like levels were increased compared with controls, and correlated with norepinephrine levels. We hypothesized that pancreastatin alongside the sympathoadrenal system might have a part in the insulin resistance of these patients, and this metabolic syndrome could play a role in the pathogenesis and complications of hypertension. In this article, we studied the normotensive offspring of these non-obese hypertensive patients and looked for metabolic abnormalities as well as plasma pancreastatin, glucagon and catecholamine levels. The subjects were separated into two groups: (1) offspring from non-insulin-resistant patients and (2) offspring from insulin-resistant patients. We found that after an intravenous glucose load, offspring from insulin-resistant patients were already hyperinsulinemic, although glucose clearance was normal, suggesting an early alteration in insulin sensitivity, whereas pancreastatin and catecholamine levels were normal compared with matched controls. However, offspring from non-insulin-resistant patients had no differences with controls. These results suggest that pancreastatin and catecholamines may not play an important role in triggering insulin resistance, although they may be important once the syndrome is established.

Journal of Endocrinology (1997) 153, 313–318

ABSTRACT

Anterior pituitary glands were removed from male rats at 5, 10, 15, 18, 21, 28, 30, 40, 45, 50 and 90 days of age, and the multiple forms of FSH present within them were separated by polyacrylamide gel–isoelectric focusing (PAGE–IEF; pH range 3·0–8·0). Gel eluents were analysed for FSH content by radioimmunoassay (RIA) and a specific radioreceptor assay (RRA). All pituitaries studied exhibited one or more peaks of immunoactive FSH within a pH range of 7·0–3·0; the major peak exhibited an isoelectric point (pi) of 4·9–4·0. Between 25 and 56% of anterior pituitary FSH obtained from rats 5–30 days old focused within a pH range of 4·9–4·5, whilst in older animals (≥40 days) this pH range contained 17–27% of the total FSH recovered. In contrast, in animals 40–90 days old, the greatest proportion of immunoactive FSH (42–62% of the total immunoactivity recovered) focused within a pH range of 4·4–4·0; further, only these groups of animals exhibited a significant proportion of anterior pituitary FSH with a pI ≤3·9. Between 14 and 21% of total FSH from 5- to 30-day-old rats focused within a pH range of 5·4–5·0, whereas in older animals this pH range contained 6–9% of the total FSH recovered. These shifts in FSH pI occurred at the time of appearance of spermiogenesis, at 45 days of age.

Although the ratio of the concentration of FSH measured by RRA to that measured by RIA declined as the pI of the anterior pituitary FSH decreased throughout a pH range of 7·0–4·0, the most acidic FSH molecules (pI <4·0) showed an abrupt increase in that ratio.

These results demonstrate that the transition from sexual immaturity to adulthood is accompanied by qualitative changes of intracellular pituitary FSH. They contrast with previous findings in female rats in which a shift to less acidic anterior pituitary FSH forms was detected at the time of vaginal opening, thus indicating the existence of a sexual dichotomy in terms of the action of gonadal steroids on the type of FSH molecule synthesized by the anterior pituitary gland.

J. Endocr. (1986) 110, 539–549

Two different estrogen receptors (ER-alpha and ER-beta) have been described, which are differentially involved in regulating the normal function of reproductive tissues. ER-alpha was considered for a long time to be the only estrogen receptor, and it has been detected in the stromal cells of the human prostate but not in the epithelium. To obtain new information about the differential effects of both receptor types, we have investigated their localization in normal prostates, benign prostatic hyperplasia (BPH), and prostatic cancer (PC) by immunohistochemistry, ELISA and Western blot. Epithelial immunostaining was absent in normal prostates and was present in BPH (10% of cells) and PC (80% of cells), whereas about 15% of stromal cells were positively immunostained for ER-alpha in the three types of prostatic specimens studied. Epithelial immunostaining for ER-beta was detected in normal prostates (13% of cells), BPH (30% of cells) and PC (79% of cells), whereas stromal immunostaining for ER-beta was absent in normal and hyperplastic prostates and was present in PC (12% of cells). The complementary presence of both receptor types in the normal prostate (ER-beta in the epithelium and ER-alpha in the stroma) might explain the mechanism of estrogen action in the development of BPH. The increased epithelial immunostaining for both ER-alpha and ER-beta in BPH and PC suggests that the involvement of estrogen receptors in hyperplasia and cancer concerns mainly the epithelium.

Regulators of G-protein signaling (RGS proteins) interact with Gα subunits of heterotrimeric G-proteins, accelerating the rate of GTP hydrolysis and finalizing the intracellular signaling triggered by the G-protein-coupled receptor (GPCR)–ligand interaction. Angiotensin II (Ang II) interacts with its GPCR in adrenal zona glomerulosa cells and triggers a cascade of intracellular signals that regulates steroidogenesis and proliferation. On screening for adrenal zona glomerulosa-specific genes, we found that RGS4 was exclusively localized in the zona glomerulosa of the rat adrenal cortex. We studied RGS4 expression and regulation in the rat adrenal gland, including the signaling pathways involved, as well as the role of RGS4 in steroidogenesis in human adrenocortical H295R cells. We reported that RGS4 mRNA expression in the rat adrenal gland was restricted to the adrenal zonal glomerulosa and upregulated by low-salt diet and Ang II infusion in rat adrenal glands in vivo. In H295R cells, Ang II caused a rapid and transient increase in RGS4 mRNA levels mediated by the calcium/calmodulin/calmodulin-dependent protein kinase and protein kinase C pathways. RGS4 overexpression by retroviral infection in H295R cells decreased Ang II-stimulated aldosterone secretion. In reporter assays, RGS4 decreased Ang II-mediated aldosterone synthase upregulation. In summary, RGS4 is an adrenal gland zona glomerulosa-specific gene that is upregulated by aldosterone secretagogues, in vivo and in vitro, and functions as a negative feedback of Ang II-triggered intracellular signaling. Alterations in RGS4 expression levels or functions may be involved in deregulations of Ang II signaling and abnormal aldosterone secretion.

Abstract

The antiprogesterone RU486 injected on the morning of pro-oestrus blunts the preovulatory secretion of LH and FSH and abolishes the secondary secretion of FSH during oestrus without affecting ovulation in the rat. To ascertain whether the secretion of LHRH is involved in these effects, we studied the effects of RU486 (4 mg/0·2 ml oil), given s.c. at 0800 h on pro-oestrus, on LHRH secretion into the pituitary stalk blood vessels and on peripheral plasma concentrations of LH and FSH at 1800 h on pro-oestrus and 0200 h on oestrus. Furthermore, we determined the effects of an s.c. injection of 1 mg of an LHRH antagonist (LHRH-A; ORG30276) at 2000 h on pro-oestrus and those of an i.p. injection of 100 ng LHRH (Peninsula 7201) at 0100 h on oestrus on serum concentrations of LH, FSH and oestradiol at 0200 h on oestrus in oil- and RU486-treated rats.

RU486 decreased LHRH secretion at 1800 h on prooestrus while this was increased at 0200 h on oestrus. While the reduction of preovulatory LHRH secretion in RU486-treated rats coincided with a reduction in both LH and FSH surges during the evening of pro-oestrus, the increased LHRH secretion during the early hours of oestrus was only accompanied by an increased concentration of LH. An injection of LHRH stimulated, while that of LHRH-A inhibited serum concentrations of LH at 0200 h on oestrus in both oil- and RU486-treated rats. An injection of LHRH-A had no effect on FSH concentration at 0200 h on oestrus in either oil- or RU486-treated rats. On the contrary, exogenous LHRH increased FSH concentration at 0200 h on oestrus only in oil-treated rats.

The results indicate that, in the rat, progesterone secretion during the afternoon and evening of pro-oestrus enhances preovulatory LHRH and suppresses LHRH release during early oestrus into the pituitary stalk blood vessels on the afternoon of pro-oestrus and during early oestrus respectively. While the secretion of LH during early oestrus is blunted by progesterone and entirely coupled to LHRH secretion, the secondary secretion of FSH during oestrus is not dependent on endogenous LHRH and at the same time is completely dependent on the actions (direct and/or indirect) of progesterone.

Journal of Endocrinology (1994) 141, 7–14

The selective oestrogen receptor modulator (SERM) tamoxifen (TX) has agonist/antagonist actions on LH secretion in the rat. Whereas in the absence of oestrogens TX elicits progesterone receptor (PR)-dependent GnRH self-priming, it antagonizes oestrogen-stimulatory action on LH secretion. The aim of these experiments was to explore whether TX treatment-induced differential expression of oestrogen receptor (ER)α and ERβ in the gonadotrope may determine its agonist effect on LH secretion. In the first experiment, basal LH secretion, GnRH-stimulated LH secretion and PR-dependent GnRH self-priming were determined in incubated pituitaries from ovariectomized (OVX) rats treated with oestradiol benzoate (EB), TX or raloxifene (RX). Cycling rats in metoestrus or pro-oestrus were used as basic controls. As in pro-oestrus, pituitaries from OVX rats treated with EB exhibited GnRH-stimulated LH secretion, immunohistochemical PR expression and GnRH self-priming. While RX had no effect on these parameters, TX induced PR expression and GnRH self-priming. GnRH self-priming was absent in pituitaries incubated with the antiprogestin ZK299. In the second experiment, we evaluated the immunohistochemical expression of ERα and ERβ in gonadotropes of cycling rats and OVX rats treated with EB, TX or RX. We found that while ERα expression was similar in all six groups, ERα expression was oestrous cycle dependent. Moreover, ERα expression in gonadotropes of TX-treated rats was as high as that found in pro-oestrus, while ERα expression in the gonadotropes of RX-treated rats was lower than in metoestrous or pro-oestrous pituitaries. These results suggest that, in the absence of the cognate ligand, TX, unlike RX, may regulate LH secretion through the ERα subtype in gonadotropes.

Suppression of TSH release from the hypothyroid thyrotrophs is one of the most rapid effects of 3,3′,5′-triiodothyronine (T₃) or thyroxine (T₄). It is initiated within an hour, precedes the decrease in TSH β mRNA inhibition and is blocked by inhibitors of mRNA or protein synthesis. TSH elevation in primary hypothyroidism requires both the loss of feedback inhibition by thyroid hormone in the thyrotrophs and the positive effects of TRH. Another event in this feedback regulation may be the thyroid hormone-mediated induction of the TRH-inactivating pyroglutamyl peptidase II (PPII) in the hypothalamic tanycytes. This study compared the chronology of the acute effects of T₃ or T₄ on TSH suppression, TRH mRNA in the hypothalamic paraventricular nucleus (PVN), and the induction of tanycyte PPII. In wild-type mice, T₃ or T₄ caused a 50% decrease in serum TSH in hypothyroid mice by 5 h. There was no change in TRH mRNA in PVN over this interval, but there was a significant increase in PPII mRNA in the tanycytes. In mice with genetic inactivation of the type 2 iodothyronine deiodinase, T₃ decreased serum TSH and increased PPII mRNA levels, while T₄-treatment was ineffective. We conclude that the rapid suppression of TSH in the hypothyroid mouse by T₃ occurs prior to a decrease in TRH mRNA though TRH inactivation may be occurring in the median eminence through the rapid induction of tanycyte PPII. The effect of T₄, but not T₃, requires the type 2 iodothyronine deiodinase.