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ABSTRACT

Interleukin-1 (IL-1) has been proposed as a paracrine regulator of testicular function. The effect of this cytokine on adult rat Leydig cells in primary culture was investigated. Interstitial cells were purified on a two-step Percoll gradient and cultured in the presence or absence of recombinant human IL-1α (IL-1α). The presence of IL-1α in the culture media resulted in a dose-dependent increase in 24-h basal androgen release (half-maximal effective concentration = 40–50 U/ml). The stimulatory effect of IL-1α peaked on days 3 and 4, and was often still significant after 6 days of culture. Removal of IL-1α was followed by a return of basal androgen release to control levels within 3 days. In contrast, cells treated with IL-1α (100 U/ml) for 3 days released significantly less androgen (per 4 h) in response to 1–100 ng LH/ml than control cells. A similar inhibitory effect on the response to dibutyryl cAMP and pregnenolone was observed. Under basal conditions, IL-1α-treated cells released significantly more cAMP than did control cells. In contrast, the increase in cAMP release seen with LH-stimulated cells was significantly inhibited by treatment with IL-1α. These results suggest that IL-1α has a dual effect on adult rat Leydig cells in culture. It stimulates basal but inhibits LH-induced androgen release with parallel changes in cAMP levels. An additional inhibitory effect appears to lie at the level of the 17α-hydroxylase/C17–20 lyase enzyme.

Journal of Endocrinology (1991) 129, 381–390

ABSTRACT

Lactating ewes were treated with murine epidermal growth factor (EGF) and its effects on concomitant milk production and composition were observed. Six ewes were infused via the jugular vein with 200 ml saline/day over 4 days (days 9–12 of lactation) followed by EGF at a dose rate of 0·5 mg/day in 200 ml saline over 4 days (days 13–16). All ewes then received a further infusion of 200 ml saline/day over 4 days (days 17–20). During the experiment a maintenance (lactation) diet was offered and ewes were machine-milked twice daily.

An EGF-immunoreactive material was detected in mammary secretions and urine throughout the experiment, but only in plasma (1–9 μg/l) during the period of EGF infusion. The amount of EGF appearing in milk and urine increased from 37 μg and 10 μg respectively (day 1 of EGF infusion) to 56 μg and 17 μg respectively (day 4). EGF treatment resulted in lower milk yield and reduced concentration of lactose and protein; milk fat concentration fell after EGF infusion had ceased. Water intake increased markedly during EGF infusion and was 60% (4 kg) greater on day 4 than that measured during the first saline infusion. Urine volume also increased and was 164% (3·6 kg) greater by day 4 of EGF infusion compared with that recorded in the first saline infusion. Water retention (intake minus output in milk, urine and faeces) was significantly higher on the day after EGF infusion ceased than that found during the first saline infusion. The possibilities that the increased water intake was primary, or secondary, to a diuretic effect of EGF are discussed.

Journal of Endocrinology (1992) 132, 377–385

ABSTRACT

Sex differences in the hourly values of serum LH were examined in male and female Syrian hamsters exposed to either long photoperiods (14 h light: 10 darkness; 14L: 10D) or short photoperiods (6L: 18D). In long photoperiods, females exhibited a pro-oestrous surge of LH in response to high levels of circulating oestradiol (1047·36 ± 90·68 pmol/l), while LH values in male hamsters remained essentially constant. In females housed in short photoperiods oestradiol levels were reduced by fivefold; however, a discrete surge in serum LH, similar to that seen at pro-oestrus in females exposed to long photoperiods, was observed. Although exposure to a short photoperiod eliminates the requirement of a positive feedback of oestrogen for the expression of an afternoon surge in LH, male hamsters housed in short photoperiods showed no indication of an afternoon surge in serum LH. These observations indicate that sex differences in the neural control of LH release are not the result of sex differences in oestrogen sensitivity or responsiveness.

J. Endocr. (1984) 100, 101–105

Abstract

Five lactating goats were infused, via an external pudic arterial catheter, directly into the mammary gland with 0·9% (w/v) NaCl (20 ml/h), recombinant human insulin-like growth factor-I (IGF-I; 80 nmol/h), recombinant human IGF-II (133 nmol/h) or IGF-I and IGF-II combined. The infusion was for 6 h and milk yield was determined every 2 h. The ratio of milk yield in the infused relative to the non-infused gland was changed only slightly by saline (2%), but increased to 9% (P<0·05) in response to IGF-I and 8% (P<0·05) in response to IGF-II. When combined, both peptides increased this ratio by 6%. These effects were elicited within 2–4 h of the beginning of infusion. Mammary blood flow increased 50–80% (P<0·05) during all IGF infusions, but only 28% during saline treatment. Plasma insulin decreased 50% (P<0·01) during the infusion of IGF-I alone or in combination with IGF-II and 25% in response to IGF-II alone. Whereas plasma glucose increased by approximately 10% during infusion of IGF-I alone or with IGF-II, it was not altered by infusion of IGF-II only.

The rapidity and unilateral nature of the milk-yield response to IGF-I and IGF-II is consistent with their acting directly on mammary tissue itself. Thus, the present results demonstrate similar local and systemic actions induced by intramammary infusion of IGF-II and IGF-I, although the magnitude of the response to IGF-II tends to be less than that to IGF-I.

Journal of Endocrinology (1994) 142, 93–99

Abstract

The effect of insulin-like growth factor-I (IGF-I) administration on body weight gain and the rate of recovery of renal function was investigated in rats following an acute episode of renal ischaemia. Since the des(1–3)IGF-I and LR³IGF-I variant forms of IGF-I have been shown to be more potent than IGF-I, their effects were also examined. Acute renal failure was produced in male Sprague–Dawley rats by clamping both renal arteries for 45 min. Treatment was commenced at the time of renal artery occlusion with vehicle (0·1 mol acetic acid/l; control group), IGF-I (2·0 mg/kg per day), des(1–3)IGF-I (2·0 mg/kg per day) or LR³IGF-I (1·5 mg/kg per day) by s.c. osmotic pump, and continued for 7 days, with rats being held in metabolism cages. Glomerular filtration rate (GFR) was estimated by the use of ⁵¹Cr-EDTA continuously infused i.p. via osmotic pump. Following the episode of renal ischaemia, body weight gain and nitrogen retention were significantly improved in all three peptide-treated groups, and serum urea concentrations were reduced in the groups treated with IGF-I and des(1–3)IGF-I. However, there was no evidence of the variants having any increased potency over the growth effects of IGF-I itself. GFR was significantly reduced, urine output was increased and urinary concentrating ability was reduced in all groups compared with normal rats, with no significant effect of the IGF peptides being apparent.

A closer examination of the acute effects of LR³IGF-I on renal function was undertaken by measuring GFR for 3 days before and 3 days after renal ischaemia in two groups of rats, treated for the latter 3 days with either vehicle (controls) or LR³IGF-I (1·5 mg/kg per day). LR³IGF-I treatment following renal ischaemia resulted in a significantly greater fall in GFR than in controls, urinary osmolality was also significantly reduced, and fractional excretion of sodium was increased. In addition, there was histological evidence of a greater degree of tubular epithelial calcification in the kidneys of the rats treated with LR³IGF-I.

This study showed that administration of IGF peptides at doses sufficient to cause significant improvement in anabolic status did not improve renal function in rats following an acute episode of renal ischaemia. Indeed the LR³IGF-I variant of IGF-I had a deleterious effect on renal function in the early stage of the recovery period.

Journal of Endocrinology (1994) 140, 23–32

ABSTRACT

The metabolic clearance of ovine insulin-like growth factor-II (IGF-II) was examined in sheep using ¹³¹I-labelled IGF-II. Following i.v. administration the tracer was distributed in a volume similar to that of the vascular space (58-5 ±3.3 ml/kg; mean ± s.e.m., n = 5) and demonstrated a triphasic pattern of clearance. Size-exclusion chromatography of a plasma sample collected 1 min after injection revealed peaks of radioactivity corresponding to hormone complexed to binding proteins of 150 and 40–50 kDa (relative abundance 21 and 65% respectively), a high molecular weight binding protein (>200 kDa; 5%) and 'free' tracer (9%). Chromatography of sequential plasma samples revealed different patterns of clearance for these constituents. Half-lives of ¹³¹I-labelled IGF-II complexed to the 150 and 40–50 kDa binding proteins, as calculated from rate constants for their decay, were 351 ± 30 and 9.6 ± min respectively (n = 5). These differ markedly from estimates for the clearance of IGF-I (545 ± 25 min, n = 8, and 34 ± 2.3 min, n = 6) associated with carrier proteins of the same apparent molecular weights. This was reflected in calculated metabolic clearance rates for IGF-I (3.9 ± 0.5 ml/min) and IGF-II (7.8 ±1.0 ml/min). Chromatography also revealed that free IGF-II was reduced to negligible levels by 12 min. In contrast, radioactivity eluting in the position expected for the > 200 kDa binding protein was cleared from the circulation very slowly. However, the small proportion of total radioactivity eluting in these molecular weight regions precluded calculation of decay constants for these species. Tracer degradation was monitored throughout the clearance study and estimated to be <20% at 800 min following i.v. administration. Less than 20% of tracer was cleared into urine over the 24 h of sampling, concurrent with a >90% fall in plasma radioactivity. Tracer in urine was completely degraded.

Journal of Endocrinology (1989) 123, 461–468

ABSTRACT

Clearance of protein-bound forms of insulin-like growth factor-I (IGF-I) from the circulation of sheep was determined using single injections of ¹³¹I-labelled ovine or [Thr⁵⁹]-human IGF-I, in the 'free' form or prebound to 50 or 150 kDa plasma binding protein fractions. The half-life of circulating protein-bound forms of IGF-I was determined by size-exclusion chromatography of plasma samples taken over a 24-to 26-h experimental period.

IGF-I bound to lower molecular weight binding protein(s) (approximately 50 kDa) showed a half-life of 26–40 min (mean 34 min; n = 6), while the half-life of a high molecular weight fraction (150 kDa) was considerably longer (range 398–603 min; mean 545 min; n =8). Metabolic clearance of IGF-I following administration of free tracer ranged from 3.0 to 5.3 ml/min in sheep (n = 4) weighing 26.0–28.5 kg. Tracer distribution volume was 59 ml/kg liveweight (n=4).

Tracer degradation products were first detected in plasma 8 h after i.v. administration. No differences in stability of the purified ovine and recombinant human IGF-I tracer preparations were observed. However, a fraction of the [Thr⁵⁹]-IGF-I tracer did not possess binding activity and this was associated with excretion of a greater proportion of administered radioactivity (over 22 h) in urine in animals receiving [Thr⁵⁹]-IGF-I tracer (18.4–19.3%) compared with ovine IGF-I (7.1–11.0%).

Following administration of free tracer or tracer bound to the 50 kDa protein, the proportion of radioactivity bound to the 150 kDa fraction increased over the first 20-30 min of observation. However, this was not apparent following administration of tracer bound to the 150 kDa protein, indicating that the more rapid turnover of IGF-I bound to the 50 kDa protein was associated, in part, with transfer of IGF-I to the 150 kDa binding protein fraction.

The calculated secretion rates of the IGFs were two- to threefold and twentyfold higher, for IGF-I and -II respectively, relative to that of insulin. These data are evidence supporting roles for IGFs in the regulation of metabolism.

Journal of Endocrinology (1989) 123, 469–475

ABSTRACT

The infusion of low doses of epidermal growth factor (EGF) into lactating ewes stimulates water intake and urine volume. The plasma concentrations and daily output of various electrolytes in milk and urine are also affected. We have investigated this further by recording the effects of EGF infusion on fluid balance, electrolyte profiles and plasma concentrations of glucose and parathyroid hormone (PTH) in non-pregnant, non-lactating ewes. Twenty-four animals (n= 8 per group) received infusions of 100 ml saline/day into the jugular vein for 10 days (days 1–10) followed by EGF at a dose rate of either 1 (low dose), 5 (medium dose) or 10 (high dose) μg/kg liveweight per day in 100 ml saline for 5 days (days 11–15). All ewes then received an infusion of 100 ml saline/day for 10 days (days 16–25).

Most plasma and urine samples had undetectable concentrations of EGF-immunoreactive material during the periods of saline infusion. During EGF infusion, the highest amounts of EGF infusate excreted in urine were 1·6, 5·9 and 5·6% for ewes in low, medium and high dose groups respectively. Water intake increased by 17% (0·5 kg), 88% (2·5 kg) and 89% (2·3 kg) and urine volume increased by 29% (0·5 kg), 108% (2·2 kg) and 134% (2·1 kg) for the three groups respectively. Fluid balance and feed intake were not affected by EGF infusion, but the output of faecal dry matter was reduced in ewes receiving the two higher doses of EGF.

All levels of EGF resulted in hypocalcaemia, increased plasma PTH concentrations and hypermagnesaemia. There was no effect of EGF on plasma concentrations of K⁺ and glucose or on daily urinary excretion of K⁺ and Mg²⁺. The only response to the low dose was a reduced plasma concentration of Na⁺ and an increased daily urinary urate excretion. The two higher doses increased the daily urinary excretion of Na⁺, PO₄ ³⁻ and urate, but had no effect on the respective concentrations in plasma. Urinary Ca²⁺ excretion was reduced only during infusion of the medium dose of EGF.

The responses of most variables were similar during infusion of the medium and high doses of EGF. All three doses of EGF induced polydipsic and diuretic responses in ewes, and infusions of 5–10 μg EGF/kg liveweight per day affected renal excretion of Ca²⁺, Na⁺ and PO³⁻ ₄. We interpret the responses of the kidney and plasma PTH concentrations as a means of maintaining the homeostasis of plasma profiles of electrolytes.

Journal of Endocrinology (1992) 135, 91–101