Leptin, adiposity, and testosterone in captive male macaques.

Leptin is considered to act as a signal relating somatic energetic status to the reproductive system. However, the nature of that signal and its relationship with male reproductive function across nonhuman primate species are unclear. We suggest that species-specific differences in leptin physiology may be related to the degree of environmental variation and variation in the importance of energy stores for male reproduction. In order to test the role of seasonality in species differences among nonhuman primates, we compared leptin, testosterone, and body composition in male rhesus (n = 69) and pig-tailed (n = 43) macaques. Despite having larger abdominal fat deposits, the rhesus macaques did not exhibit significantly higher leptin levels (rhesus, 2.21 +/- 0.43 ng/ml; pig-tailed, 2.12 +/- 0.39 ng/ml). Both species showed increases in leptin across adolescent, subadult, and adult age-groups (P = 0.036 for rhesus; P = 0.0003 for pig-tailed by ANCOVA). Testosterone was not significantly associated with leptin in either the rhesus (r = 0.039; P = 0.754) or pig-tailed (r = 0.2862; P = 0.066) samples. Comparison of leptin levels across the two species using univariate modeling procedures showed no significant age-group by abdominal fat interaction. These findings suggest little difference in leptin production between these two closely related species, despite the difference in breeding seasonality.

Dehydroepiandrosterone-sulfate as a biomarker of senescence in male non-human primates.

Numerous studies have suggested important and varying roles for dehydroepiandrosterone (DHEA) and dehydroepiandrosterone-sulfate (DHEA-S) in primate physiological functions. Despite these numerous claims, specific actions and significance of DHEA and DHEA-S are still equivocal. A decline of these hormones in adult humans may have functional significance, yet there is no clear relationship between functional impairments of aging and the decline in DHEA or DHEA-S levels. This current study attempts to address the natural history of adrenal hormones by presenting non-human primate evidence of the endocrinology of aging; the age-related patterns of adrenal hormone decline in three species of the subfamily Cercopithecinae, Macaca mulatta, Macaca nemestrina, and Papio cynocephalus are compared. It is concluded that DHEA-S and cortisol represent lineage specific markers of senescence among primates and that parallel age-related patterns of DHEA-S and cortisol likely reflect lineage specific effects, or rather, phylogenetic similarities of endocrine senescence. The use of relative adrenal hormone levels to approximate species' life expectancies is discussed.

Morphological and hormonal parameters in two species of macaques: impact of seasonal breeding.

To compare physiological and developmental differences between two cogeneric species that differ by seasonal vs. aseasonal breeding, values for morphological measurements, testicular volume, serum testosterone, estradiol, and dehydroepiandrosterone-sulfate levels were obtained from 53 rhesus during the early breeding season, as well as 41 pig-tailed macaque males maintained at the Tulane Primate Center. The two species exhibited similar body size, testosterone, and estradiol levels, but differed substantially in testicular volume (3.00 +/- 1.7 vs. 1.72 +/- 1.3 cc), abdominal skinfold measures (15.7 +/- 9.2 vs. 9.0 +/- 7.7 mm), and DHEA-S levels (18.0 +/- 11.7 vs. 7.6 +/- 5.4 microg/dl). Significant interaction effects for species by age group were found for weight, tricep circumference, length, and estradiol level. In addition, length was more closely related to testicular volume among rhesus compared to pig-tailed macaques, suggesting different developmental patterns between the species. Predictors of hormonal levels differed between the two species. In the rhesus, estradiol levels were related to testicular volume and testosterone levels while there were no anthropometric predictors of testosterone or DHEA-S. For the pig-tailed macaques, testicular volume was related to tricep circumference, testosterone to triceps skinfold and testicular volume, and estradiol to weight. It is argued that rhesus have larger testes for body size and more abdominal fat deposits during the early breeding season relative to pig-tailed macaques reflecting the increased demands of sperm competition in a seasonally breeding species. Hormonal differences associated with the difference in breeding system appear to be primarily related to adrenal rather than testicular activity.

Food puzzle for singly caged primates.

To enhance environmental complexity for singly caged pigtailed macaques (Macaca nemestrina), we designed a food puzzle to promote foraging. The puzzles, made of clear plastic tubing and loaded with peanuts in the shell, were suspended from linked chains and attached to the fronts of the cages. Animals manipulated the puzzles by reaching through a cage opening. Upon presentation of loaded puzzles, most animals attempted to remove the peanuts. More peanuts were removed within an hour after the puzzle was loaded than at any other time during the day. Young adult animals showed no sex differences in number of peanuts removed and were more proficient than middle-aged animals in removing peanuts during the first hour of testing. Middle-aged females were more proficient than middle-aged males. The food puzzle enhanced the animals' cage environment by providing a goal-oriented activity that they could control. © 1992 Wiley-Liss, Inc.