The Effects of Prostaglandin Synthetase Inhibitor Indomethacin on the Hypothalamic and Neurohypophysial Oxytocin Content in Euhydrated and Dehydrated Male White Rats¹)

Abstract

Rats euhydrated or dehydrated up to eight days were given intraperitoneally indomethacin (IM) twice daily in a dose of 0.2 mg/100 g of initial body weight. A single dose of IM injected to euhydrated animals did not affect the neurohypophysial oxytocic activity but decreased that potency in the hypothalamus. When IM was administered repeatedly during four or eight days, the hypothalamic oxytocic activity did not differ from the respective controls; under such conditions the oxytocic activity in the neurohypophysis increased progressively. Under conditions of dehydration the known depletion of hypothalamic and neurohypophysial oxytocin storage was not affected by indomethacin. It is therefore suggested that impulses of osmoreceptor origin are of distinct importance in determining the function of oxytocinergic neurones under conditions of inhibited prostaglandin synthesis.

Inhibition of Prostaglandin Synthesis and the Release of Vasopressin and Oxytocin from the Rat Neurohypophysis: In Vitro Studies1)

“…The present study shows that indomethacin, included in the incubation medium, can inhibit both the basal and K-evoked release of vasopressin and oxytocin from the neurointermediate lobe in vitro. These findings are in agreement with recent reports from this laboratory (Bojanowska et al, 1985;Guzek et al, 1986), i.e. with demonstration of increased vasopressin and oxytocin storage (due possibly to inhibition of neurohormonal release) in the neurohypophysis under chronic treatment with indomethacin in vivo.…”

“…In other experiments, however, the intracerebroventricular treatment with indomethacin failed to affect the plasma vasopressin in the dog (Brooks et al, 1984;Hoffman et al, 1982;Yamamoto et al, 1978). When administered intraperitoneally, indomethacin was recently reported to rise the neurohypophysial vasopressor (Bojanowska et al, 1985) and oxytocic (Guzek et al, 1986) activities in the rat. The effects of indomethacin on the release of neurohypophysial hormones in vivo seem therefore to be not consistent so far.…”

Prostaglandin F2 alpha Stimulates Vasopressin and Oxytocin Release from Isolated Rat Neurointermediate Lobe1)

“…Meclofenamate (Walker, 1983) as well as indomethacin (Yamamoto et al, 1978;Hoffman et al, 1982) were noted to decrease the vasopressin secretion in the dog. Indomethacin was observed to increase the vasopressin and oxytocin content in the neurohypophysis of the rat (Bojanowska et al, 1985;Guzek et al, 1986). In in vitro experiment, indomethacin diminished the vasopressin output from guinea-pig hypothalamo-neurohypophysial system to angiotensin II or hypertonic medium (Ishikawa et al, 1981).…”