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In an attempt to establish whether the gonadotrophic hormones are secreted in a pulsatile mode during neonatal development in the rhesus monkey, four infantile males were bilaterally gonadectomized at 1–2 weeks of age. Sequential blood samples were taken 22–36 days later from each animal every 10 min for 3–4 h during the light phase of the 24-h light: darkness cycle and circulating LH concentrations were determined by radioimmunoassay. Plasma concentrations of this gonadotrophin fluctuated dramatically and in an apparently rhythmic fashion with peaks recurring at approximately hourly intervals. These findings indicate that by the neonatal stage of ontogeny the hypothalamic-hypophysial apparatus which governs gonadotrophin secretion in this species is capable of generating a pulsatile or episodic pattern of LH release.
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Few data are available on the metabolism of progesterone in infra-human primates. Using gas chromatography, Chamberlain, Knights & Thomas (1964) detected 5β-pregnane-3α,20α-diol in the urine of pregnant rhesus monkeys and in the urine of a male injected with a large dose of progesterone, although quantitative data were lacking. While it would appear that the metabolism of progesterone in an anthropoid ape, such as the chimpanzee, is similar to that in man (Romanoff, Grace, Sugarman & Pincus, 1963), the observations of Jeffery (1966) have indicated that this may not be the case in a catarrhine monkey. We have therefore studied the excretion of progesterone metabolites in the urine and faeces of the rhesus macaque (Macaca mulatta).
Five adult, female rhesus monkeys (4·6–7·1 kg. body weight) each received approximately 25 [4-14C]progesterone i.v. (Table 1), and were then placed either in primate restraining chairs or metabolism cages in order to make
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SUMMARY
Labelled progesterone was administered intravenously to five, adult female rhesus monkeys and urine and faeces were collected every 24 h. Excretion of radioactivity in urine occurred most rapidly in the first 24-h period and then declined exponentially. The excretion of radioactivity in faeces reached maxima during the 2nd, 3rd or 4th 24-h periods depending on the animal studied. 76–94% (mean 86%) of the radioactivity administered was recovered within 9 days, but small quantities continued to be excreted in urine up to 16 days after injection. Generally, greater amounts of radioactivity were recovered from faeces (41–57%) than from urine (26–48%). Using different hydrolytic and extraction procedures, some 50% of the radioactivity in urine was recovered in the neutral extracts. The major metabolite in urine was androsterone which accounted for 1·1–12·2% (mean 6·0%) of the progesterone administered. Pregnanediol was not an important urinary catabolite in this species. Differences in the extent to which progesterone is metabolized to C-19 compounds in macaques, baboons, great apes and man may reflect the phylogeny of a catabolic desmolase system in anthropoid primates.
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It is known that the frequency of ejaculation by male rhesus monkeys shows a well-marked annual rhythm under laboratory conditions (Michael & Keverne, 1971). Recent studies have demonstrated that a major component of the sexual behaviour of the male is androgen-dependent (Wilson, Plant & Michael, 1972; Michael, Wilson & Plant, 1973; Phoenix, Slob & Goy, 1973). We have estimated plasma testosterone in a group of fully adult male rhesus monkeys throughout the year, and during this time they were routinely mated with oestrogen-treated, ovariectomized females.
Eight adult male rhesus monkeys (7·6–12·3 kg body wt) were obtained from India. They were quarantined in London for periods of 4–10 months before shipment to the U.S.A. Here they were housed in individual cages in an air-conditioned animal room where lighting was rigorously controlled to give 14 h light/day between 06.15 and 20.15 h. Blood was collected from the saphenous vein and plasma testosterone
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SUMMARY
The assays of testosterone and corticosteroids in plasma from adult male rhesus monkeys using competitive protein-binding and radioimmunoassay techniques are described. The radioimmunoassay for testosterone was conducted without chromatography and, therefore, additionally estimated 17β-hydroxy-5α-androstan-3-one (dihydrotestosterone). Levels of testosterone in the peripheral plasma of 14 intact male rhesus monkeys showed marked fluctuations over a period of 24 h. Concentrations of testosterone at 22.00 h (1776 ± 814 ( ± s.d.) ng/100 ml) were approximately double those at 08.00 h (858 ± 407 ng/100 ml), 12.00 h (898 ± 316 ng/100 ml) and 16.00 h (784 ± 530 ng/100 ml). Castration resulted in low plasma testosterone levels (85 ± 29 ng/100 ml), and the increases at 22.00 h were no longer observed. In intact males, the 'basal' plasma corticosteroidlevel(08.00 h) was 22·4 ± 6·0 μg/100 ml. Administration of synthetic corticotrophin raised plasma corticosteroid levels without changing plasma testosterone concentration. Because plasma testosterone levels were not related to changes in adrenocortical activity, the noctural rises appear to be due to changes in testicular secretion.
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This study examined the ontogeny of the testicular testosterone response to precocious pulsatile LH stimulation in the juvenile rhesus monkey. LH stimulation was achieved with an i.v. infusion (one pulse every 3 h) of either single-chain human (sch)LH, administered alone or in combination with recombinant human (rh)FSH, or recombinant monkey (rm)LH in combination with rmFSH. Homologous gonadotropin treatment resulted in an adult profile of circulating mLH concentrations. The schLH infusions produced a similar pulsatile pattern in circulating LH with peak concentrations of approximately 5 IU/l. Although a robust testicular testosterone response was observed after 24 h of intermittent LH stimulation, surprisingly testosterone release at this time was continuous. The apulsatile mode of testosterone secretion, however, did not persist, and a switch to an unequivocal episodic mode of secretion, comparable to that observed in adult monkeys, occurred by day 4 of LH stimulation. FSH did not influence the pattern of the testosterone response. We conclude from these findings that progenitor Leydig cells in the primate testis are able to respond rapidly to a physiological LH stimulus. While the cell biology underlying the switch from a continuous to a pulsatile mode of testosterone secretion remains unclear, we suggest that this phenomenon may be related to the hypothesis that episodic testosterone secretion is required for the operation of the neuroendocrine axis governing testicular function.
