ABSTRACT

Diurnal concentrations of serum melatonin were determined longitudinally in female rhesus monkeys throughout sexual maturation to ascertain how levels varied with advancing age and reproductive onset. Females were housed either in outdoor enclosures (n = 8) exposed to ambient environmental conditions, or indoors (n = 4) under a photoperiod of 12 h light: 12 h darkness and fixed temperature of 20–23 °C. Animals were studied from immaturity (15 months) through first ovulation and were additionally compared with fully adult female rhesus monkeys (n = 5) studied during the annual breeding season. The diurnal melatonin pattern was described for the developing females in the summer, autumn and winter in 3 successive years from samples collected at 10.00, 18.00, 22.00, 02.00, 06.00 and 10.00 h.

Nocturnal levels of melatonin declined significantly during development in both indoor- and outdoor-housed females with a progressive decrease up to 33 months of age. Daytime values were consistently low but exhibited a slight decline also with age. Nocturnal values in all months sampled fell significantly with greater decreases occurring at the earliest ages. Furthermore, superimposed upon this developmental change, animals housed outdoors responded to seasonal changes in photoperiod with diurnal increases in melatonin occurring after sunset. The females in the present study exhibited first ovulation at two distinct ages: 32–37 months ('early', n = 6) and 41–45 months ('later', n=5). One female did not ovulate within the study period. Although nocturnal levels of serum melatonin were similar between the two groups up to 29 months of age, a post-hoc analysis revealed that concentrations were significantly lower by 34 months of age for the early group, a time coincident with first ovulation. Nocturnal levels of melatonin remained high, relative to the early group, in the later ovulating females until 43 months of age, coincident with first ovulation for these animals. The diurnal pattern of serum melatonin at first ovulation, regardless of chronological age, was similar to that observed during the ovulatory season for adult female rhesus monkeys.

These data suggest that nocturnal melatonin concentrations decline with advancing chronological age in prepubertal female rhesus monkeys. Furthermore, the timing of sexual maturation was inversely related to nocturnal melatonin. Whether this change in melatonin is causally related to reproductive onset or, rather, is a consequence of other factors regulating the occurrence of first ovulation remains to be determined. Furthermore, the observation that the melatonin rhythm in outdoor-housed females follows the prevailing photoperiod permits the hypothesis that this rhythm may mediate any photoperiodic effect on the seasonal occurrence of first ovulation characteristic of rhesus monkeys housed outdoors.

Journal of Endocrinology (1989) 121, 553–562

ABSTRACT

Nocturnal concentrations of melatonin in serum decline significantly with advancing pubertal development in both children and non-human primates and elevated levels may be associated with anovulation in adults. Three studies, using female rhesus monkeys, were performed to determine whether (1) the decline in nocturnal melatonin concentrations in adolescents was due to maturational increases in serum oestradiol, (2) the experimental elevation in nocturnal melatonin would delay the normal progression of puberty in post-menarchial monkeys, and (3) the experimental elevation in nocturnal melatonin would disrupt normal ovulatory function in adults. In experiment 1, juvenile female rhesus monkeys, housed indoors in a fixed photoperiod (12 h light: 12 h darkness), were assigned randomly to one of two treatment groups: ovariectomized with no replacement therapy (control; n= 4) or ovariectomized with oestradiol replacement therapy maintaining oestradiol at ∼ 90 pmol/l (treated; n= 8). Twenty-four hour as well as daytime serum samples were collected from 19 to 35 months of age. Nocturnal melatonin concentrations declined significantly in all females with advancing chronological age and this change was unaffected by oestradiol treatment. The decline in nocturnal melatonin concentrations occurred, on average, 2·0 ±0·2 months after the initial rise in serum LH in control females and 6·0 ±0·8 months in treated females. Furthermore, this decline in night-time melatonin was not related to significant developmental changes in body weight.

In experiment 2, control (n = 6) and melatonintreated (treated; n =6) adolescent female monkeys were studied from −30 to +105 days from menarche. Beginning at 45 days following menarche, treated females received 30 days of nocturnal melatonin infusion to elevate levels to prepubertal values. Developmental changes in perineal swelling and coloration as well as serum oestradiol and insulin-like growth factor-I (IGF-I) were compared with values observed during the 45-day pretreatment and 30-day post-treatment conditions as well as with those observed in control females. Despite a significant elevation in nightly melatonin levels for the 30-day period in treated females, developmental changes in oestradiol, IGF-I, and perineal coloration and swelling were not different compared with the control females.

In experiment 3, adult females were given melatonin nightly beginning on the first day of menses following an ovulatory cycle and treatment was continued for 45 days or until the next menstruation occurred. Melatonin was elevated to supraphysiological levels every night throughout the treatment period. Despite this elevation, an ovulation, inferred from serum progesterone levels, occurred in every female and serum oestradiol, LH or progesterone were not affected compared with the values obtained during the untreated cycle.

These data indicate that the decline in nocturnal melatonin concentrations is not related to a developmental increase in oestradiol secretion. Furthermore, experimentally elevated concentrations of nocturnal melatonin did not delay the normal progression of puberty following menarche nor did it disrupt ovulatory function in adults. These data suggest that the enhanced nocturnal melatonin concentrations are not causally linked to either puberty onset or anovulatory conditions in adults.

Journal of Endocrinology (1993) 137, 299–309

ABSTRACT

The effects of oestradiol (OE₂) on adolescent growth in female rhesus monkeys were evaluated by testing the hypothesis that, upon removal of the ovary, the increase in growth normally seen at the time of puberty would be abolished and that treatment with OE₂ would restore it. Juvenile monkeys (n= 12) were ovariectomized and were given either an OE₂-bearing silicone elastomer capsule implanted subcutaneously to simulate mid-pubertal concentrations ('treated = ', n = 8) or no steroid treatment ('control = ', n = 4). Females were studied from 18 to 42 months of age which, in intact females, typically encompasses the prepubertal period to the occurrence of first ovulation. Over the whole period, growth in body weight, crown–rump (CR) length and tibia length for control females were less than the 95% confidence limits of females treated with OE₂. However, significant spurts of growth in both CR and tibia length occurred in the control as well as treated animals, although the peak velocities were somewhat lower for non-OE₂-treated animals. Peak growth velocities occurred at an earlier chronological age in treated females, although at the same degree of skeletal maturity as found in control females. Skeletal maturity was significantly advanced in treated females from 27 months onward. Serum concentrations of nocturnal GH increased significantly with advancing age in both groups, with greater increases observed in treated females. Serum concentrations of IGF-I were higher in treated females until some 30 months of age, at which point concentrations increased in a similar fashion in both groups. IGF-I concentrations were elevated in the months preceding and following the peak CR growth velocity in treated females whereas concentrations of IGF-I rose coincidently with peak CR growth in control females. These data indicate that, in the absence of OE₂, growth in female monkeys has periods of acceleration and that OE₂ may enhance this pre-set pattern. Furthermore, the growth-promoting effects of OE₂ are determined by the degree of skeletal maturity. Once a certain degree of skeletal maturity is attained, bones may be primed for maximal growth, but, as skeletal maturity continues to advance, the effect of OE₂ on growth diminishes.

Journal of Endocrinology (1993) 137, 519–527

SUMMARY

Concentrations of cortisol and testosterone in the plasma of adult male rhesus monkeys living in social groups were determined during a 27-h period. Capture and venipuncture of experienced, conditioned animals did not lead to a fall in the concentration of testosterone in the plasma during the 90 min immediately after removal from the group. Both plasma cortisol and plasma testosterone concentrations showed a significant fall and rise in samples collected every 3 h during a 27-h period, even though there was considerable individual variation. During the autumn breeding season, animals showed higher concentrations of testosterone at both 10.00 and 22.00 h compared with those observed at the same times during the summer. Even though animals demonstrated significant diurnal changes, testosterone samples withdrawn at the same time of day (10.00 h) on consecutive days were significantly correlated with one another (r = 0·65, n = 27, P < 0·01), suggesting the usefulness of sampling once a day to study potential environmental influences on plasma testosterone concentrations.

Two forms of prolactin (Prl), prolactin 177 (Prl₁₇₇) and prolactin 188 (Prl₁₈₈), are produced in the rostral pars distalis (RPD) of the pituitary gland of euryhaline Mozambique tilapia, Oreochromis mossambicus. Consistent with their roles in fresh water (FW) osmoregulation, release of both Prls is rapidly stimulated by hyposmotic stimuli, both in vivo and in vitro. We examined the concurrent dynamics of Prl₁₇₇ and Prl₁₈₈ hormone release and mRNA expression from Prl cells in response to changes in environmental salinity in vivo and to changes in extracellular osmolality in vitro. In addition, mRNA levels of Prl receptors 1 and 2 (prlr1 and prlr2) and osmotic stress transcription factor 1 (ostf1) were measured. Following transfer from seawater (SW) to FW, plasma osmolality decreased, while plasma levels of Prl₁₇₇ and Prl₁₈₈ and RPD mRNA levels of prl ₁₇₇ and prl ₁₈₈ increased. The opposite pattern was observed when fish were transferred from FW to SW. Moreover, hyposmotically induced release of Prl₁₈₈ was greater in Prl cells isolated from FW-acclimated fish after 6 h of incubation, while the hyposmotically induced increase in prl ₁₈₈ mRNA levels was only observed in SW-acclimated fish. In addition, prlr2 and ostf1 mRNA levels in Prl cells from both FW- and SW-acclimated fish increased in direct proportion to increases in extracellular osmolality both in vivo and in vitro. Taken together, these results indicate that the osmosensitivity of the tilapia RPD is modulated by environmental salinity with respect to hormone release and gene expression.

ABSTRACT

The influence of gonadal status on the pattern of changes in body weight was examined in three groups of outdoor-housed premenarchial rhesus monkeys (Macaca mulatta) from 1 to 2 years of age. Gonadally intact (n=8) and ovariectomized oestradiol-treated females (n=5) gained significantly more weight than ovariectomized untreated females (n=5). The overall larger weight gains for the intact and ovariectomized oestradiol-treated groups were associated with significantly higher fasting levels of serum insulin. All subjects exhibited two periods of significant weight gain from 12 to 16 months of age between May and September and from 21 to 24 months of age between February and May. Serum GH and somatomedin-C levels were also raised during these periods of accelerated growth. Although the pattern of serum GH was similar among groups, serum somatomedin-C levels were significantly higher in both intact and ovariectomized oestradiol-treated subjects from 21 to 24 months of age, suggesting physiological levels of oestradiol may facilitate somatomedin-C production during periods of increased GH secretion. Thus, absolute changes in body weight in outdoor-housed premenarchial rhesus monkeys are influenced by gonadal status, possibly mediated through increases in serum insulin. Furthermore, dynamic changes in body weight occur during prepubertal development, with the largest increments associated with increased somatomedin-C levels at specific ages synchronized with natural changes in the environment.

J. Endocr. (1984) 102, 311–317

Aquaporins (Aqps) are expressed within key osmoregulatory tissues where they mediate the movement of water and selected solutes across cell membranes. We leveraged the functional plasticity of Mozambique tilapia (Oreochromis mossambicus) gill epithelium to examine how Aqp3, an aquaglyceroporin, is regulated in response to osmoregulatory demands. Particular attention was paid to the actions of critical osmoregulatory hormones, namely, prolactin (Prl), growth hormone and cortisol. Branchial aqp3 mRNA levels were modulated following changes in environmental salinity, with enhanced aqp3 mRNA expression upon transfer from seawater to freshwater (FW). Accordingly, extensive Aqp3 immunoreactivity was localized to cell membranes of branchial epithelium in FW-acclimated animals. Upon transferring hypophysectomized tilapia to FW, we identified that a pituitary factor(s) is required for Aqp3 expression in FW. Replacement with ovine Prl (oPrl) was sufficient to stimulate Aqp3 expression in hypophysectomized animals held in FW, an effect blocked by coinjection with cortisol. Both oPrl and native tilapia Prls (tPrl₁₇₇ and tPrl₁₈₈) stimulated aqp3 in incubated gill filaments in a concentration-related manner. Consistent with in vivo responses, coincubation with cortisol blocked oPrl-stimulated aqp3 expression in vitro. Our data indicate that Prl and cortisol act directly upon branchial epithelium to regulate Aqp3 in tilapia. Thus, within the context of the diverse actions of Prl on hydromineral balance in vertebrates, we define a new role for Prl as a regulator of Aqp expression.

SUMMARY

The pineal indole 5-methoxytryptophol (ML) has been shown to have an antigonadal activity when administered to experimental animals, but data on its normal pattern of secretion have been lacking. Using a new gas chromatography–mass spectrometry assay, the concentration of ML at various phases of the human menstrual cycle has been studied. Daily samples were obtained throughout the month from five women with a normal cycle and two women taking an oral contraceptive. In women with a normal cycle levels of ML were found to be significantly lower in the last third of their cycle; this change was not seen in women taking an oral contraceptive who had low levels throughout the month. The changes in concentration of ML did not correlate with the changes in concentration of gonadotrophins.