Oxytocin stimulates LH production by the anterior pituitary gland of the rat.
Gonadotrophin-releasing activity of oxytocin has previously been demonstrated in vitro and in vivo. This study investigated whether oxytocin is also able to induce LH accumulation in pituitary cells. Following trypsin digestion and mechanical dispersion, pituitary cells from female rats were incubated with oxytocin (100 nmol/l) for 24 h. LH release stimulated by oxytocin increased (P less than 0.001) progressively during the incubation indicating a different secretory pattern from the more rapid but less sustained secretion stimulated by gonadotrophin-releasing hormone. Oxytocin also enhanced (P less than 0.01) total LH accumulation in the incubation system (released plus cell contents) which was apparent after 7-11 h of stimulation. The release of LH stimulated by oxytocin was reduced by the protein synthesis inhibitor cycloheximide (10 mumol/l). However, cycloheximide did not completely block oxytocin-stimulated LH release; there remained some LH release above that seen in nonstimulated controls (P less than 0.01) revealing the presence of a cycloheximide-resistant component in the release mechanism. Furthermore, accumulation of total LH in 24 h incubations was suppressed (P less than 0.01) by cycloheximide. The advancement in LH release which oxytocin has been shown to induce in vivo in pro-oestrous rats was accompanied by an early reduction of pituitary LH stores. However, the fall normally observed in LH content during the surge was markedly attenuated by the oxytocin treatment. Thus, loss of pituitary LH stores was less in oxytocin-treated rats than in saline-treated controls, even though net LH release into plasma was increased. Therefore, oxytocin stimulated the replenishment of LH stores.(ABSTRACT TRUNCATED AT 250 WORDS)
Robinson
G
G
University Department of Obstetrics and Gynaecology, Christchurch Women's Hospital, New Zealand.
Evans
J J
JJ
Catt
K J
KJ
D000818:Animals; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D005260:Female; D007986:Luteinizing Hormone / Q000032:analysis / Q000096:biosynthesis*; D008297:Male; D010121:Oxytocin / Q000494:pharmacology*; D010902:Pituitary Gland / Q000737:chemistry / Q000166:cytology; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013268:Stimulation, Chemical
D010121:Oxytocin; D007986:Luteinizing Hormone; D003513:Cycloheximide