Determination of bioactive FSH in rhesus monkeys (Macaca mulatta)

Studies of the reproductive biology of nonhuman primates are commonly hindered by the lack of homologous, sensitive immunoassay systems for gonadotropins. The recent development of a bioassay based upon folliclestimulating hormone (FSH)‐stimulated estradiol production by rat Sertoli cells (Padmanabhan et al.: Endocrinology 121:1089–1098, 1987) offers a novel opportunity to expand our knowledge of the physiological importance and regulation of this important reproductive hormone in these species. Accordingly, we have established the utility of the rat Sertoli cell FSH bioassay to study the reproductive biology of rhesus monkeys. Analysis of medium from cultured rhesus monkey pituitary cells demonstrates the ability of this assay system to specifically and sensitively detect macaque FSH. Serial dilutions of unextracted urinary samples stimulate estradiol in parallel with the reference standard. The pattern of bioactive FSH in daily urine samples throughout the menstrual cycle resembles that normally observed in serum, displaying a clear preov alatory gonadotropin surge. In attempts to analyze rhesus monkey serum, severe interference with cellular estradiol production was found with extremely low serum sample volumes. In order to circumvent this problem, a serum extraction procedure utilizing metaphosphoric acid was developed which permits the accurate determination of bioactive FSH in serum. The pattern of serum bioactive FSH secretion throughout the menstrual cycle is in general agreement with that observed by FSH RIA, although immunoreactive FSH values are consistently higher. The ability to detect bioactive FSH in macaques will significantly enhance our research capabilities with nonhuman primate species which share many physiological similarities with man. Important applications also may be found in studies on the reproductive biology in endangered species of primates.