Influence of in vivo reproductive endocrine state on growth hormone- releasing factor stimulated adenylate cyclase activity in anterior pituitary fragments

Steven M. Gabriel, Edward H. Hunnicut, William J. Millard, Tltomas M. Badger, James A. Nathanson

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

The growth hormone releasing factor (GRF) stimulated adenylate cyclase activity was evaluated in membrane fractions of anterior pituitary glands from male and female rats and in gonadectomized rats following in vivo gonadal steroid treatments. The baseline adenylate cyclase activity was lower in random estrous cycle female rats as compared with males. When estrous cycle phases were evaluated, diestrus 1 females had a lower basal activity as compared with males, while proestrus females were similar to males. The maximal stimulation of adenylate cyclase activity by GRF (i.e. Vmax) was lower in random estrous cycle female rats than in males. This lower Vmax, relative to males, was more pronounced in diestrus I than in proestrus females. There was little difference in the ED50 for GRF-stimulated adenylate cyclase activity among these groups. The adenylate cyclase activity was altered 1 week after gonadectomy or 1 week after gonadectomy plus simultaneous in vivo gonadal steroid treatment. The expression of data as a function of whole tissue (content) or as a function of protein (concentration) influenced magnitude and direction of these treatment effects. This may reflect the proliferation of nonsomatotroph cell populations and altered protein synthetic activity following reproductive endocrine manipulations. When expressed as a whole tissue content, the baseline adenylate cyclase activity was unchanged after gonadectomy when compared to same-sex, gonadal-intact cohorts. However, an increase in the Vmax for GRF-stimulated adenylate cyclase activity was found in gonadectomized rats relative to sham-operated, gonadal-intact cohorts. When the same data were calculated relative to protein concentration, a decrease in baseline was found following orchidectomy, but not following ovariectomy, when compared to sham-operated, gonadal-intact cohorts. The corresponding Vmax for these groups, expressed as a concentration, decreased after orchidectomy, but increased after ovariectomy. Gonadectomy plus estrogen treatment decreased both baseline and Vmax for GRF-stimulated adenylate cyclase activity. This potent decrease was evident when compared to either same-sex, gonadectomized, or gonadal-intact cohorts for both forms of data expression. Basal and maximally stimulated adenylate cyclase activities following ovariectomy plus testosterone treatment were similar to gonadal-intact females when the data were expressed as a content, but similar to ovariectomized rats when the same data were expressed as a concentration. None of the above treatments significantly altered the ED50 for GRF-stimulated adenylate cyclase activity. These data indicate sex differences for in vitro basal and GRF- stimulated adenylate cyclase activity in rat anterior pituitary membranes. With heterotypic in vivo steroid treatment, estrogen was inhibitory, while testosterone partially was stimulatory to basal and GRF-stimulated adenylate cyclase activity.

Original languageEnglish
Pages (from-to)63-69
Number of pages7
JournalNeuroendocrinology
Volume57
Issue number1
DOIs
StatePublished - 1993
Externally publishedYes

Keywords

  • Adenylate cyclase
  • Estrogen
  • Growth hormone
  • Growth hormone releasing factor
  • Testosterone

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