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A Possible Role of Prostacyclin to Stimulate Prolactin and Growth Hormone Release by Hypothalamic and Pituitary Actions, Respectively^*

Department of Physiology, University of Texas Health Science Center at Dallas 5323 Harry Hines Boulevard, Dallas, Texas 75235
Institute of Pathophysiology, University Medical School of Szeged Szeged, H-6701 Hungary

Address requests for reprints to: S. M. McCann, M.D., Department of Physiology, University of Texas Health Science Center at Dallas, 5323 Harry Hines Boulevard, Dallas, Texas 75235.

Abstract

Prostacyclin (PGI₂) (1–5 µg in 3 µl 0.05 M Tris/HCl buffer, pH 7.5) and its stable metabolite, 6-oxo-PGF₁, were microinjected into the third ventricle of ovariectomized rats, and plasma FSH, GH, PRL, and TSH levels were measured by RIA. Control animals received 3 µl buffer. Injection of 5 µg PGI₂ dramatically elevated plasma PRL values (4- to 5-fold) at 5 and 15 min, whereas the same dose of 6-oxo-PGF₁ produced a significant but smaller (2-fold) stimulatory effect. A delayed increase (1.5-fold) in plasma GH occurred after intraventricular PGI₂ at 30 and 60 min. 6-Oxo-PGF₁ failed to alter GH levels. There were no alterations in plasma FSH and TSH after intraventricular injection of PGI₂. Dispersed, overnight cultured cells from anterior pituitaries of ovariectomized rats were tested with 10^–4-10^–7 M PGI₂ and its metabolite. After 15 min of incubation, 3 x 10_–5 PGI₂ produced a highly significant elevation in GH release (P < 0.001), whereas there was no alteration in PRL levels. Only pharmacological doses of 6-oxo-PGF₁ (10^–4 M) stimulated GH release. There was no alteration in PRL release by the cultured cells even in the presence of 10^–4 PGI₂. These results suggest that PGI₂ stimulates PRL release by a hypothalamic action either to increase the release of PRL-releasing factor, or to decrease release of PRL-inhibiting factor, or by both mechanisms. The delayed stimulatory effect of PGI₂ on the release of GH may be exerted via an effect on the anterior lobe itself, since PGI₂ was effective in stimulating GH release by the incubated pituitary cells. (Endocrinology 114: 359, 1984)

Footnotes

^* This work was supported by NIH Grants HD-09988 and AM-10073.

Received August 9, 1983.