Stimulation of hypothalamic prolactin release by veratridine and angiotensin II in the female rat: effect of ovariectomy and estradiol administration.
In the female rat immunoreactive prolactin (IR-PRL) has been identified in the hypothalamus and in other brain regions. Brain IR-PRL is not of pituitary origin and, based on polyacrylamide gel electrophoresis and peptide mapping, shares a high degree of sequence homology with its pituitary counterpart. We have previously shown that hypothalamic tissue can release IR-PRL in vitro when depolarized by potassium. In this study, we examined the release of IR-PRL from hypothalami obtained from intact and ovariectomized rats and incubated in the presence of veratridine (an alkaloid which depolarizes excitable membranes), angiotensin II, or thyrotropin-releasing hormone. Hypothalamic tissue spontaneously released IR-PRL, and this release was significantly increased by veratridine or angiotensin II in a dose-dependent manner. The specificity of the angiotensin-II-evoked IR-PRL release was demonstrated by the inhibitory effect of saralasin, an angiotensin II receptor antagonist, on hypothalamic IR-PRL release. Thyrotropin-releasing hormone (100 microM) had no effect on hypothalamic IR-PRL release. Ovariectomy decreased hypothalamic IR-PRL content and IR-PRL release in response to veratridine and angiotensin II. The effect of estradiol on hypothalamic IR-PRL content and release was also examined by obtaining hypothalami from ovariectomized rats injected with estradiol (1 microgram/day) or vehicle for 5 days. When compared with vehicle injected rats, administration of estradiol significantly increased the hypothalamic IR-PRL content (46 +/- 4 vs. 81 +/- 16 ng/mg protein).(ABSTRACT TRUNCATED AT 250 WORDS)
DeVito
W J
WJ
Division of Endocrinology, University of Massachusetts Medical School, Worcester.
Stone
S
S
Avakian
C
C
D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D007031:Hypothalamus / Q000187:drug effects* / Q000378:metabolism; D066298:In Vitro Techniques; D010052:Ovariectomy; D010053:Ovary / Q000502:physiology*; D011388:Prolactin / Q000378:metabolism*; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains; D012084:Renin-Angiotensin System / Q000502:physiology; D014701:Veratridine / Q000494:pharmacology*
D000804:Angiotensin II; D004958:Estradiol; D014701:Veratridine; D011388:Prolactin