Endothelin-like immunoreactivity in lactotrophs, gonadotrophs, and somatotrophs of rat anterior pituitary gland are affected differentially by ovarian steroid hormones.
It has been previously found that all hormone-producing phenotypes of the anterior lobe of the pituitary gland are capable of producing endothelin (ET)-like substances. The aim of this study was to determine whether the expression of ET-1-like peptides in lactotrophs, gonadotrophs, and somatotrophs is influenced by different in vivo ovarian hormonal conditions. Anterior lobes of the pituitary gland were harvested from ovariectomized and ovarian steroid-replaced adult female rats 10-12 d after surgery. Quantitative immunocytochemistry was performed on enzymatically dispersed pituitary cells. The presence of ET-1-like immunoreactivity in prolactin-, luteinizing hormone-, or growth hormone-producing cells was demonstrated by double-label immunocytochemistry. The incidence of ET-1 immunopositive pituitary cells was unaffected by progesterone treatment alone. Estradiol replacement caused a modest decrease in the number of lactotrophs and somatotrophs expressing ET-1 but increased the incidence of ET-1 immunopositive cells among gonadotrophs. Combined treatment with estradiol and progesterone robustly increased the incidence of ET-1 immunopositive lactotrophs and gonadotrophs but had no effect on somatotrophs. These data reveal that the synthesis of ET-1-like peptides in lactotrophs and gonadotrophs (and, to a lesser extent, in somatotrophs) is sensitive to ovarian steroids. Furthermore, these findings predict that ovarian steroids modulate ET-1 biosynthesis during the estrous cycle, suggesting a possible mechanism by which the ovarian steroid milieu may regulate the responsiveness of lactotrophs and gonadotrophs to their hypothalamic secretagogues.
Kanyicska
B
B
Department of Biological Science, Florida State University, Tallahassee 32306-4340, USA. bela@neuro.fsu.edu
Lerant
A
A
Freeman
M E
ME
D000818:Animals; D004343:Drug Implants; D019332:Endothelin-1 / Q000032:analysis*; D004958:Estradiol / Q000008:administration & dosage / Q000494:pharmacology*; D005260:Female; D005455:Fluorescent Antibody Technique; D005640:Follicle Stimulating Hormone / Q000032:analysis; D013006:Growth Hormone / Q000032:analysis*; D007150:Immunohistochemistry; D007986:Luteinizing Hormone / Q000032:analysis; D010052:Ovariectomy; D010903:Pituitary Gland, Anterior / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism; D011374:Progesterone / Q000008:administration & dosage / Q000494:pharmacology*; D011388:Prolactin / Q000032:analysis*; D051381:Rats; D017207:Rats, Sprague-Dawley
D004343:Drug Implants; D019332:Endothelin-1; D011374:Progesterone; D004958:Estradiol; D011388:Prolactin; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D013006:Growth Hormone