Estrogen action on growth hormone in pituitary cell cultures from adult and juvenile macaques

Basal growth hormone (GH) levels are higher in female than male primates, and estradiol (E) treatment of gonadectomized primates increases serum GH. To determine if the effect of E is mediated at the level of the somatotroph, we verified the effect of E-treatment on serum GH in spayed macaques, and then examined the effect of E on GH secretion in serum-free monkey pituitary cultures. Daily blood samples were obtained from cynomolgus macaques which were spayed upon detection of menstruation and immediately implanted with either empty (n = 5) or E-filled (n = 5) 2-cm silastic capsules. The average level of GH was significantly higher (P < 0.003) in the E-treated group than in the control group (6.4 ± 0.7 vs. 3.7 ± 0.6 ng/ml). Pituitaries from rhesus monkeys were dispersed and cultured in 48-well plates on extracellular matrix in DME/ F12 with insulin, transferrin, selenium. Using pituitary cells from a long-term spayed female, two plates were established with and without phenol red. Each plate was treated with E in a dose-related manner (0.001-10 nM) from days 0-18 (4 wells per dose). There was a significant dose-related increase in medium prolactin (PRL) in both plates, but E had no effect on GH. Therefore, the effect of E on GH in spayed monkeys cannot be accounted for by a direct action on somatotrophs. Additional phenol red-free pituitary cultures were established from four juvenile males, one adult male, two juvenile females, and two adult females and treated with E in a dose-related fashion for 28 days. Neither the adult male, the adult female, nor the juvenile female cultures exhibited an increase in GH with E treatment. Only the four juvenile male pituitary cultures showed a variable increase in GH with maximal responses ranging from 5 to 40% over control. This data suggested that the juvenile male pituitary contained an E-sensitive GH-secreting cell population which is not present in the other pituitary cultures. PRL and GH double-immunocytochemical staining of pituitary cultures from an adult female and a juvenile male revealed a significant population of rounded and possibly double-labeled cells in the juvenile male culture which were infrequently seen in the adult female culture. Speculatively, this population could represent mammosomatotroph stem cells that corelease GH and PRL upon stimulation.