Abstract

In intact cyclic ewes intrauterine infusion of conceptus secretory proteins results in the suppression of both endometrial oxytocin receptor concentrations and oxytocin-induced prostaglandin F_2α release. However, similar infusion in progesterone-treated ovariectomized ewes, while suppressing endometrial oxytocin receptors, does not fully inhibit oxytocin-induced prostaglandin F_2α release. To examine whether this anomaly resulted from an inadequate simulation of the luteal phase in the ovariectomized ewe treated with progesterone alone, the effects of additional treatment with two other ovarian hormones, oestradiol-17β and oxytocin, was investigated. Rather than permitting conceptus secretory protein to successfully inhibit oxytocin-induced prostaglandin F_2α release, treatment with oestradiol-17β in addition to progesterone actually resulted in an advancement in the timing of release. However, treatment with oxytocin, alone or in combination with oestradiol, permitted the full inhibition of oxytocin-induced prostaglandin F_2α release. To confirm that this effect did not result from the action of oxytocin alone, independently of the action of conceptus secretory protein, a second experiment was undertaken using a similar protocol but without the infusion of conceptus secretory protein. In this situation, oxytocin-induced prostaglandin F_2α release was only partially inhibited suggesting that both luteal oxytocin and conceptus secretory proteins are necessary to facilitate the full inhibition of luteolysis during early pregnancy in the ewe.

Journal of Endocrinology (1996) 150, 473–478

Plasma samples from intact, adrenalectomized, adrenalectomized and castrated and castrated bulls were assayed for LH, testosterone, androstenedione and oestradiol-17β from birth to 26 weeks of age. The adrenalectomized bulls, unlike the intact bulls, failed to show a rise in androstenedione at 14·5 weeks of age or a rise in testosterone at 20 weeks of age. Testosterone levels in the castrated animals remained below 0·4 ng/ml whereas androstenedione reached levels similar to those in intact bulls by 26 weeks of age. In all animals the concentration of oestradiol-17β in plasma remained below 25 pg/ml, although intact bulls had the highest levels. Levels of LH rose after castration but not after adrenalectomy. These data show that in bull calves absence of the adrenal glands during prepuberty delays the rise in pubertal testosterone by at least 10 weeks.

Ministry of Agriculture and Fisheries, Research Division, Ruakura Agricultural Research Centre, Hamilton, New Zealand

(Received 17 April 1978)

An increase in the plasma concentration of luteinizing hormone (LH) occurs in response to castration in bull calves aged 1–4 months; this response is of similar magnitude to that seen in cattle castrated as adults (Odell, Hescox & Kiddy, 1970). In bull calves castrated at birth, however, there is no increase in the plasma concentration of LH until after 28 days of age (Bass, Peterson, Payne & Jarnet, 1977). In other species a range of responses to castration has been reported. Gonadectomy of male guinea-pigs 0–35 days after birth produces an increase in the plasma concentration of LH similar to that observed in guineapigs castrated as adults (Donovan, ter Haar, Lockhart, MacKinnon, Mattock & Peddie, 1975). In contrast, the castration of young male macaques does not cause an immediate increase in the

SUMMARY

Hypothalamic content of gonadotrophin-releasing hormone (GnRH), serum LH and FSH, capacity of the testis to synthesize testosterone in vitro, and testicular 5-ene-3β-hydroxysteroid dehydrogenase-isomerase and 17β-hydroxysteroid dehydrogenase were measured in groups of rats at approximately 5 day intervals from birth to day 64 and at days 74 and 89. The capacity of the testes to synthesize testosterone in vitro was measured in the presence of a saturating dose of rat LH. Gonadotrophin-releasing hormone increased steadily from 0·17 ng per hypothalamus at birth to a maximum of 7 ng at day 52 and then remained constant. LH concentrations were highly variable and often exceeded adult values between days 10 and 32. After day 32 a steady rise was observed which reached adult values between days 37 and 42. FSH concentrations markedly increased from 255 ng/ml observed at birth and day 10 to a peak value of 1000 ng/ml at day 32. Subsequently there was a steady decline in FSH values until day 74 when the concentration returned to values found at birth. 5-ene-3β-Hydroxysteroid dehydrogenase-isomerase activity exhibited a rapid increase between days 12 and 19 followed by an even greater rate of increase between days 19 and 32 when adult levels were attained. 17β-Hydroxysteroid dehydrogenase activity was very low between birth and day 22. Enzyme activity began to increase at day 22 with a rapid increase in activity observed between days 37 and 58. The increase in capacity to synthesize testosterone closely followed the increase in 17β-hydroxysteroid dehydrogenase activity. The study demonstrates that during sexual maturation in the male rat, changes in serum LH and FSH do not reflect changes in hypothalamic GnRH. The appearance of Leydig cells as monitored by 5-ene-3β-hydroxysteroid dehydrogenase-isomerase activity precedes by approximately 20 days the increase in testicular capacity to synthesize testosterone in vitro. The latter coincides with the increase in 17β-hydroxysteroid dehydrogenase activity. These results suggest that 17β-hydroxysteroid dehydrogenase is a limiting factor in the ability of the testis to respond to LH stimulation.

Ministry of Agriculture and Fisheries, Ruakura Agricultural Research Station, Private Bag, Hamilton, New Zealand

(Received 23 August 1974)

The foetal adrenals are important in initiating parturition in sheep (Liggins, Fairclough, Grieves, Kendall & Knox, 1973) and goats (Thorburn, Nicol, Bassett, Shutt & Cox, 1972). Indirect evidence suggests that the foetal adrenals may be involved in the termination of pregnancy in the cow. Such evidence includes prolongation of pregnancy when foetal pituitary function is impaired (Kennedy, Kendrick & Stormont, 1957; Holm, 1958), and the induction of parturition by administering either corticotrophin (Welch, Frost & Bergman, 1973) or dexamethasone (Hunter, Welch, Fairclough, Barr & Seamark, 1974) to the foetal calf.

Comline, Silver, Nathanielsz & Hall (1973) have noted a two- to threefold increase in foetal cortisol levels in prematurely calving cows. These authors conclude that this comparatively small rise in foetal cortisol levels casts doubt on whether the foetal adrenal cortex is

Abstract

We have studied the uptake of ¹²⁵I-thyroxine (¹²⁵I-T₄) in the human choriocarcinoma cell line JAR. Uptake of ¹²⁵I-T₄ was time-dependent, stereospecific and reversible, with a saturable component of 33% after 120 min of incubation. Kinetic analysis of the initial specific uptake rates indicated the presence of a single uptake process with a Michaelis constant of 59·4 ± 13·9 nm (n=12) and maximum velocity of 0·29 ± 0·06 pmol/min per mg protein. Uptake was dependent on intracellular energy as, in the presence of 2 mm potassium cyanide, saturable uptake was reduced to 60·6 ± 8·5% (n=4) of control uptake. Uptake was also temperature-dependent. Saturable ¹²⁵I-T₄ uptake after 60 min of incubation was 26·1 ± 3·0% at 25 °C (n=6) and 27·3 ± 5·7% at 4 °C of control uptake at 37 °C. Ouabain did not inhibit ¹²⁵I-T₄ uptake indicating that the uptake was independent of the Na gradient across the cell membrane. Although T₄ uptake was stereospecific, as d-T₄ failed to inhibit ¹²⁵I-l-T₄ uptake, it was not specific for T₄, as tri-iodothyronine (T₃) and reverse T₃ also inhibited ¹²⁵I-T₄ uptake. We conclude that JAR cells have a saturable, stereospecific and reversible membrane transport mechanism for T₄ which is dependent on intracellular energy, but independent of the Na⁺ gradient across the cell membrane.

Journal of Endocrinology (1995) 146, 233–238

Abstract

The regulation of oxytocin, oestradiol and progesterone receptors in different uterine cell types was studied in ovariectomized ewes. Animals were pretreated with a progestogen sponge for 10 days followed by 2 days of high-dose oestradiol to simulate oestrus. They then received either low-dose oestradiol (Group E), low-dose oestradiol plus progesterone (Group P) or low-dose oestradiol, progesterone and oxytocin (via osmotic minipump; Group OT). Animals (three to six per time-point) were killed following ovariectomy (Group OVX), at oestrus (Group O) or following 8, 10, 12 or 14 days of E, P or OT treatment. In a final group, oxytocin was withdrawn on day 12 and ewes were killed on day 14 (Group OTW). Oxytocin receptor concentrations and localization in the endometrium and myometrium were measured by radioreceptor assay, in situ hybridization and autoradiography with the iodinated oxytocin receptor antagonist d(CH₂)₅[Tyr(Me)²,Thr⁴,Tyr-NH₂ ⁹]-vasotocin. Oestradiol and progesterone receptors were localized by immunocytochemistry.

Oxytocin receptors were present in the luminal epithelium and superficial glands of ovariectomized ewes. In Group O, endometrial oxytocin receptor concentrations were high (1346 ± 379 fmol [³H]oxytocin bound mg protein⁻¹) and receptors were also located in the deep glands and caruncular stroma in a pattern resembling that found at natural oestrus. Continuing low-dose oestradiol was unable to sustain high endometrial oxytocin receptor concentrations with values decreasing significantly to 140 ± 20 fmol mg protein⁻¹ (P<0·01), localized to the luminal epithelium and caruncular stroma but not the glands. Progesterone treatment initially abolished all oxytocin receptors with none present on days 8 or 10. They reappeared in the luminal epithelium only between days 12 and 14 to give an overall concentration of 306 ± 50 fmol mg protein⁻¹. Oxytocin treatment caused a small increase in oxytocin receptor concentration in the luminal epithelium on days 8 and 10 (20 ± 4 in Group P and 107 ± 35 fmol mg protein⁻¹ in Group OT, P<0·01) but the rise on day 14 was not affected (267 ± 82 in Group OT and 411 ± 120 fmol mg protein⁻¹ in Group OTW). In contrast, oestradiol treatment was able to sustain myometrial oxytocin receptors (635 ± 277 fmol mg protein⁻¹ in Group O and 255 ± 36 in Group E) and there was no increase over time in Groups P, OT and OTW with values of 61 ± 18, 88 ± 53 and 114 ± 76 fmol mg protein⁻¹ respectively (combined values for days 8–14). Oestradiol receptor concentrations were high in all uterine regions in Group O. This pattern and concentration was maintained in Group E. In all progesterone-treated ewes, oestradiol receptor concentrations were lower in all regions at all time-points. The only time-related change occurred in the luminal epithelium in which oestradiol receptors were undetectable on day 8 but developed by day 10 of progesterone treatment. Progesterone receptors were present at moderate concentrations in the deep glands, caruncular stroma, deep stroma and myometrium in Group O. Oestradiol increased progesterone receptors in the luminal epithelium, superficial glands, deep stroma and myometrium. Progesterone caused the loss of its own receptor from the luminal epithelium and superficial glands and decreased its receptor concentration in the deep stroma and myometrium at all time-points. There was a time-related loss of progesterone receptors from the deep glands of progesterone-treated ewes between days 8 and 14.

These results show differences in the regulation of receptors between uterine regions. In particular, loss of the negative inhibition by progesterone on the oxytocin receptor by day 14 occurred only in the luminal epithelium, but is unlikely to be a direct effect of progesterone as no progesterone receptors were present on luminal epithelial cells between days 8 and 14. The presence of oxytocin receptors in the luminal epithelium of ovariectomized ewes suggests that oestradiol is not essential for oxytocin receptor synthesis at this site. Oestradiol was able to sustain its own receptor at all sites, but high circulating progesterone was always inhibitory to oestradiol receptors. In general, oestradiol stimulated progesterone receptors in epithelial cells whereas progesterone abolished its own receptor from epithelial cells over a period of time, but had a lesser effect on stromal cells. The concentration of all three receptors is therefore differentially regulated between different uterine cell types, suggesting the importance of paracrine effects which remain to be elucidated.

Journal of Endocrinology (1996) 151, 375–393

Measurements have been made of hormonal changes relevant to salt and water balance during prolonged exposure to hypoxia to improve our understanding of the syndrome of acute mountain sickness. We have attempted to delineate the detailed inter-relationships between the renin–aldosterone and the vasopressin systems by a metabolically controlled study, involving an orthostatic stress (45° head-up tilt) and an injection of a standard dose of ACTH to test adrenal responsiveness. Three Caucasian medical students underwent a 7-day equilibration at 150 m (Lima, Peru), followed by a 6-day sojourn at 4350 m (Cerro de Pasco, Peru) and a final 7 days at 150 m. Measurements were made of sodium and potassium balance, body weight and the 24-h renal excretion of vasopressin, cortisol and aldosterone 18-glucuronide. These variables showed little change, except for that of aldosterone 18-glucuronide, which fell sharply at altitude and rebounded even more sharply on return to sea level. At altitude, basal plasma levels of renin activity and aldosterone fell, and the response to orthostasis was attenuated, but the fall of plasma renin activity, as compared to plasma aldosterone, was delayed; on return to sea level this dissociation was exacerbated with the return of normal renin responsiveness lagging behind that of aldosterone. We suggest that unknown factors which dissociate the orthodox renin–aldosterone relationship, other than the activity of the angiotensin I-converting enzyme, are operative on exposure to hypoxia.