Impact of exercise and dietary fatty acid composition from a high-fat diet on markers of hunger and satiety.

To compare the effects of both dietary fatty acid composition and exercise vs. sedentary conditions on circulating levels of hunger and satiety hormones. Eight healthy males were randomized in a 2 × 2 crossover design. The four treatments were 3 days of HF diets (50% of energy) containing high saturated fat (22% of energy) with exercise (SE) or sedentary (SS) conditions, and high monounsaturated fat (30% of energy) with exercise (UE) or sedentary (US) conditions. Cycling exercise was completed at 45% of VO(2)max for 2h daily. On the third HF day, 20 blood samples were drawn over a 24h period for each hormone (leptin, insulin, ghrelin, and peptide YY (PYY)). A visual analog scale (VAS) was completed hourly between 0800 and 2200. Average 24h leptin and insulin levels were lower while 24h PYY was higher during exercise vs. sedentary conditions. FA composition did not differentially affect 24h hormone values. VAS scores for hunger and fullness did not differ between any treatment but did correlate with ghrelin, leptin, and insulin. High saturated or unsaturated fat diets did not differ with respect to markers of hunger or satiety. Exercise decreased 24h leptin and insulin while increasing PYY regardless of FA composition.

Prolactin levels are elevated after infant carrying in parentally inexperienced common marmosets.

Alloparental behavior (parental behavior directed to nondescendant young) is pervasive among human cultures but rare among other mammals. New World primates of the family Callitrichidae, including common marmosets (Callithrix jacchus jacchus), dwell in large families and many family members carry and/or provision infants. This study experimentally characterized alloparenting in common marmosets by measuring infant retrieval and carrying outside of the context of the family group. Prolactin was measured in samples collected before and after infant exposure to determine whether elevated prolactin levels were predictive of alloparental responsiveness. Seventeen nonbreeding, parentally inexperienced, singly or peer-housed common marmosets (10 females, 7 males, 6-66 months of age) were tested repeatedly in an infant retrieval paradigm. Infant retrieval was shown by 5 out of 17 monkeys (29%) in their first test. The rate of retrieval increased to 10 monkeys (59%) by the fourth test. No significant differences in age, sex, or housing condition existed between monkeys that retrieved infants and those not retrieving. Prolactin concentrations were significantly elevated in serum obtained after testing only in monkeys that retrieved infants. Prolactin levels after infant exposure were positively related to carrying duration. A separate experiment verified that neither prolactin nor cortisol was significantly elevated in response to prolonged handling. Cortisol levels were inversely proportional to handling time. Prolactin levels were not significantly related to handling time. Our results indicate that alloparental behavior is expressed at high rates after minimal infant experience, and prolactin levels rise concomitantly with the expression of alloparental behavior in this species.

Bromocriptine administration lowers serum prolactin and disrupts parental responsiveness in common marmosets (Callithrix j. jacchus).

The influence of prolactin on parental responsiveness was investigated in eight unpaired, parentally inexperienced common marmosets (Callithrix jacchus; 6 female, 2 male). The marmosets were prescreened with infants (1-10 days of age) and required to exhibit short latency retrieval and infant carrying in at least three consecutive pretests as criterion for inclusion in this study. The marmosets were then administered the dopamine agonist bromocriptine (0.5 mg/0.5ml vehicle subcutaneously) and the vehicle alone (0.5 ml 10% ethanol solution) twice daily for 3 consecutive days in random order. Bromocriptine treatment reduced circulating prolactin to nondetectable levels. Bromocriptine treatment eliminated infant retrieval in four of the eight marmosets and was associated with significantly increased retrieval latencies and significantly reduced carrying durations in the four monkeys that continued to retrieve following bromocriptine treatment. When given the vehicle alone, the marmosets retrieved infants significantly faster than during pretests, suggesting a handling effect of the injection series. Bromocriptine treatments were associated with significantly increased movement during the tests. The results of this study indicate that prolactin and/or its regulatory neurotransmitters are involved in the control of the spontaneous display of parental responsiveness in common marmosets.

Prolactin levels during the periparturitional period in the biparental cotton-top tamarin (Saguinus oedipus): interactions with gender, androgen levels, and parenting.

Unlike biparental bird and rodent species, mating and parenting occur simultaneously in cotton-top tamarins, Saguinus oedipus, providing a unique model for examining endocrine interactions. This study was designed to determine the relationship of prolactin to testicular androgens during parenting and mating. Specifically we examined (1) the patterns of postpartum prolactin excretion in male and female tamarins with and without infant survival; (2) the relationship between androgen and prolactin levels during the periparturitional period in male tamarins; and (3) male hormonal response to the postpartum mating that occurs simultaneously with paternal care. All females showed an elevation in prolactin during the first week postpartum and when infants died, female prolactin levels decreased significantly. Infant survival during the first 15 days did not influence male levels of prolactin, cortisol, or the testicular androgens testosterone and dihydrotestosterone (DHT). Prolactin did not show an inverse relationship with any of the androgens (testosterone, DHT) studied during the postpartum period. No significant differences in hormones were found between prepartum levels and the first, second, and third 5-day blocks postpartum for all 10 males. Males who had infant-care experience showed an increase in testosterone during the first 5 days postpartum and prolactin levels correlated with the number of previous births a male had experienced. However, the most significant changes in testosterone occurred in males whose mates ovulated during the first 15 days following birth in contrast to males whose mates ovulated later than 15 days. These results indicate that unlike females, male tamarins are not showing hormonal changes in response to infants. Urinary androgens did not show an inverse relationship to prolactin in male tamarins, but were elevated concurrent with the female's fertile period.

Midcycle and luteal elevations of follicle stimulating hormone in squirrel monkeys (Saimiri boliviensis) during the estrous cycle.

Follicle stimulating hormone (FSH) has fundamental importance in reproductive function, but its cyclic pattern has not previously been described in the squirrel monkey, due primarily to the lack of a suitable assay. An homologous radioimmunoassay (RIA) based on recombinant cynomolgus FSH measured changes in serum FSH relative to patterns of bioactive luteinizing hormone (LH), estradiol, and progesterone during the estrous cycle. FSH was observed to have a sharp peak during the late follicular phase coincident with the LH surge and then rose again during the luteal phase. Estradiol was low except for the midcycle rise, suggesting an inhibitory relationship. The rat granulosa cell in vitro FSH bioassay confirmed high levels of this hormone. Measurement of FSH in the squirrel monkey has found a pattern different from Old World primates in the luteal phase, which may provide insight into the reproductive mechanisms of this species.

Skeletal effects of aging in male rhesus monkeys.

Age-related bone loss in men is receiving increased attention. In light of this, animal models for male bone loss are desirable. This study examined the effects of age and osteoarthritis (OA) on bone mineral content (BMC), bone mineral density (BMD), and markers of bone turnover and skeletal relevance in 56 male rhesus monkeys 4-34 years of age. BMC and BMD increased at all sites from 4 to 10 years of age. Male rhesus monkeys reach peak bone mass at approximately 10 years of age after which bone mass is lower at the lateral spine and distal radius. Markers of bone turnover (osteocalcin and carboxyterminal telopeptide of type I collagen [ICTP]) decreased with age. There was no relationship between PTH, 25-hydroxyvitamin D, FSH, or testosterone and age. With advancing age, the prevalence of lumbar spine OA increases dramatically, masking decreases in posteroanterior spine bone mass that are clear in the lateral projection. These data suggest that male rhesus monkeys sustain age-related bone loss in the absence of nutritional or gonadal steroid deficiencies. These animals may prove useful in studying the mechanisms of age-related bone loss.

Suppression of cortisol levels in subordinate female marmosets: reproductive and social contributions.

Socially subordinate female common marmosets (Callithrix jacchus) have markedly lower plasma cortisol levels than dominant females. Subordinate females also undergo hypoestrogenemic anovulation, and estrogen can elevate glucocorticoid levels. Therefore, we previously hypothesized that this cortisol difference is mediated by rank-related differences in reproductive hormones, probably estradiol. To test this possibility, we characterized the effects of the ovarian cycle and ovariectomy on plasma cortisol concentrations. Beginning in the early follicular phase, basal blood samples were collected from seven cycling female marmosets daily for 16 days and at 2- to 3-day intervals for another 16 days. Samples were collected identically from seven anovulatory subordinate females and seven long-term ovariectomized females. Cortisol levels changed reliably across the ovarian cycle, with levels in the mid- to late follicular, peri-ovulatory, and early luteal phases higher than those in the remainder of the cycle. Cortisol levels of cycling females were significantly higher than those of subordinates at all parts of the cycle, but were significantly higher than those of ovariectomized females only during the midcycle elevation. Unexpectedly, subordinates had significantly lower cortisol levels than ovariectomized females, as well as higher estradiol and estrone levels and lower progesterone and luteinizing hormone (LH) levels. These results confirm that circulating cortisol concentrations are modulated by reproductive function in female marmosets but also indicate that low cortisol levels in subordinate females cannot be attributed simply to hypoestrogenemia. Instead, other factors, such as direct effects of social subordination or suppression of LH levels, contribute to suppression of cortisol in subordinates.

Hormonal responses to parental and nonparental conditions in male cotton-top tamarins, Saguinus oedipus, a New World primate.

The socially monogamous cotton-top tamarin (Saguinus oedipus) monkey is a cooperative breeder with the breeding male providing extensive parental care shortly after birth. We examined the relationship of urinary prolactin and cortisol excretion both to male parental care and as a stress response in the cotton-top tamarin monkey. First-morning urine samples were collected to determine hormonal concentrations. Hormonal and behavioral data were collected on 8 male cotton-top tamarins during the 2 weeks before and the 2 weeks following birth of infants to their mate, 11 nonparental males with exposure to females, and three eldest sons from large family groups. Prolactin levels were significantly higher in experienced fathers during the postpartum period than in the other males, while cortisol levels were significantly lower in experienced fathers and eldest sons. Prolactin levels in experienced fathers were consistently elevated before birth, following birth, and after infants were weaned; prolactin levels during times of infant independence were still significantly higher than those in nonfather males. First-time fathers exhibited prolactin levels that were significantly higher after the births of infants than these same males did when they were paired with nonpregnant females. Elevated prolactin concentrations also occurred prior to the first birth, suggesting that males may be receiving cues from their pregnant females. The elevated prolactin levels in parental males may be associated with the experience of the fathers. Correlation between prolactin levels and number of successful births, number of previous births, and age were high. The care of newborn infants did not appear to be a stressful event since cortisol levels were not elevated postpartum. Both cortisol and prolactin were elevated following capture and injection of saline or a dopaminergic receptor antagonist, indicating that prolactin does respond to acute stress. Cortisol levels did not coincide with prolactin levels except under acute stress conditions, suggesting that different neural pathways are probably involved in prolactin release during parental care versus acute stress. These studies provide evidence that male urinary prolactin levels may be elevated due to cues from pregnant females and the constant exposure of males to the family environment.

Social and reproductive influences on plasma cortisol in female marmoset monkeys.

Subordinate female common marmosets (Callithrix jacchus) undergo ovulation suppression and exhibit low plasma cortisol levels compared to the dominant, breeding female. To determine whether this cortisol difference is mediated by the differential reproductive consequences of social status, we monitored plasma progesterone and cortisol in 32 adult female marmosets while they were housed in heterosexual pairs, during the first 3 days of heterosexual group formation, and while animals were housed in established social groups. Cortisol levels prior to group formation were significantly higher in females exhibiting cyclic ovulatory activity than in anovulatory females but were not predictive of social status. Subsequently, when animals were housed in established social groups, dominant (cyclic) females had significantly higher cortisol levels than did subordinate (anovulatory) females. Cortisol levels differed between the pre and postgroup formation conditions only in animals that underwent a corresponding onset or termination of ovulatory cyclicity. Cortisol differences between dominant and subordinate female marmosets therefore appear to be associated with differences in reproductive function rather than with social status per se.