Prostaglandin F2 alpha-stimulated release of ovarian oxytocin in the sheep in vivo: threshold and dose dependency.
To determine the threshold of prostaglandin F2 alpha (PGF2 alpha)-stimulated oxytocin secretion from the ovine corpus luteum, low levels of PGF2 alpha (5-100 pg/min) were infused into the ovarian arterial blood supply of sheep with ovarian autotransplants. PGF2 alpha was infused for six sequential 10-min periods at hourly intervals, 6, 12, or 24 days after estrus (n = 3 for each day). Each cycle day was studied during a separate cycle. Oxytocin and progesterone in ovarian venous and carotid arterial plasma was measured by radioimmunoassay, and secretion rates were determined (venous-arterial concentration x plasma flow). In animals treated on Day 6, 5 pg/min PGF2 alpha caused a significant release of oxytocin (p less than 0.01), whereas in animals treated on Day 12, this threshold was 40 pg/min (p less than 0.05). In animals treated on Day 24, the threshold for oxytocin release was greater than 100 pg/min. PGF2 alpha did not significantly change ovarian blood flow or progesterone secretion rate on any day (p greater than 0.05). To determine residual luteal oxytocin after each threshold experiment, 5 mg PGF2 alpha was given i.m. to all animals. Significantly more oxytocin was released by Day 6 than by Day 12 and Day 24 corpora lutea, and by Day 12 than by Day 24 corpora lutea (1.2 micrograms, 0.7 microgram, and 0.3 microgram, respectively; p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)
Lamsa
J C
JC
Worcester Foundation for Experimental Biology, Shrewsbury, Massachusetts 01545.
Kot
S J
SJ
Eldering
J A
JA
Nay
M G
MG
McCracken
J A
JA
D000818:Animals; D015237:Dinoprost / Q000502:physiology*; D005260:Female; D010053:Ovary / Q000378:metabolism* / Q000637:transplantation; D010121:Oxytocin / Q000378:metabolism*; D011374:Progesterone / Q000097:blood; D011863:Radioimmunoassay; D012756:Sheep
D011374:Progesterone; D010121:Oxytocin; D015237:Dinoprost