Alteration by histamine of the sympathetic nerve-mediated contractions in the bovine ovarian follicle wall in vitro

Effect of histamine and histamine analogues on human isolated myometrial strips

1. The effect of histamine and histamine H1- and H2-receptor agonists on isolated myometrium strips of premenopausal women has been examined. The effect of acetylcholine was also determined. 2. Histamine, 2-pyridylethylamine, 4-methylhistamine and acetylcholine, but not dimaprit, produced a concentration-related contractile response in human isolated myometrial strips. Histamine also produced a further contraction in human isolated myometrial strips precontracted with KCl (55 mM). 3. The contractile response to histamine was antagonized by the histamine H1-receptor antagonist, clemizole (0.1 microM) but was potentiated by the histamine H2-receptor antagonist, ranitidine (10 microM). Clemizole (0.1 nM to 10 nM) competitively antagonized the contractile effect of 2-pyridylethylamine (- log KB = 10.5 +/- 0.5). The concentration-response curve for acetylcholine was displaced to the right by atropine 0.1 microM. 4. Atropine (0.1 microM), propranolol (0.1 microM), prazosin (0.1 microM) and indomethacin (1 microM) failed to modify the contractile response to histamine. 5. In human isolated myometrial strips precontracted with KCl (55 mM), clemizole at 1 microM completely abolished the contractile response to histamine and revealed a concentration-dependent relaxation. Dimaprit alone and 4-methylhistamine (in the presence of clemizole), produced concentration-related relaxation with a magnitude similar to that in response to histamine. The relaxant response to dimaprit was antagonized by ranitidine. 6. It is concluded that human isolated uterine strips possess histamine H1- and H2-receptors: the former mediating contraction and the latter relaxation. The predominant response to histamine in this tissue is contraction.

Prejunctional alpha 2-adrenoreceptors modulate the stimulated release of noradrenaline in isolated follicle strips from bovine ovaries

1. Strips from the follicle wall of bovine ovaries were incubated in Krebs-Ringer solution containing 3H-noradrenaline for measurement of transmitter liberation during electrical field stimulation (5 Hz frequency, 1 ms pulse duration, 10 V between the electrodes). The effects of noradrenaline as well as selective alpha-adrenoreceptor agonists and antagonists were studied on the electrically induced efflux of radioactivity. 2. Noradrenaline (1 microM) inhibited the stimulated release of radioactivity. The alpha 2-adrenoreceptor agonist, oxymetazoline, significantly reduced the release of radioactivity in concentrations as low as 0.01 microM. The alpha 1-adrenoreceptor agonist, phenylephrine (0.01-1 microM), was without significant effect. 3. Phentolamine (0.01-1 microM) and the selective alpha 2-adrenoreceptor antagonist, idazoxan (0.01-1 microM) significantly enhanced the electrically evoked release. The alpha 1-adrenoreceptor antagonist, prazosin (0.01-1 microM), was without effect. Idazoxan (0.1 microM) reversed the inhibitory effect of oxymetazoline (0.1 microM). 4. It is concluded that administration of noradrenaline or the alpha 2-adrenoreceptor agonists reduces the release of labelled noradrenaline by acting on prejunctional alpha 2-adrenoreceptors in the noradrenergic nerves distributed in the wall of the bovine ovarian follicle. This is one of several prejunctional receptor mechanisms that modulate the activity of the sympathetic nerves innervating the smooth musculature of the follicle wall.

GABA suppresses stimulation-induced release of [3H]-noradrenaline from sympathetic nerve fibres in bovine ovarian follicles

1 Strips from the bovine ovarian follicle wall were incubated in Krebs-Ringer solution containing [3H]-noradrenaline in order to saturate sympathetic nerve fibres with radiolabelled transmitter. This allowed the study of field stimulation-evoked transmitter release. 80.3 +/- 3.9% of the tritium released upon stimulation (10 Hz, pulse duration 1 ms, 10 V between the electrodes) was noradrenaline. 2 The stimulated release of tritium was totally blocked in calcium-free, EGTA (1 mM) containing medium or by 1 microM tetrodotoxin. Chemical sympathectomy (6-hydroxydopamine treatment) in vitro reduced the tritium content of the strip by 85%. The neuronal amine uptake blocker desipramine (0.6 microM) was almost equally effective in inhibiting the incorporation of tritium. The extraneuronal amine uptake blocker normetanephrine (10 microM) reduced the tritium content by 30%. Together, the results suggest that the electrically evoked release of tritium reflects the release of [3H]-noradrenaline from sympathetic nerve fibres. 3 gamma-Aminobutyric acid (GABA) concentration-dependently reduced the electrically evoked tritium release. Also the GABAB-receptor agonist baclofen (30 microM) reduced the stimulated tritium release whereas muscimol (100 microM), a GABAA-receptor agonist, failed to affect the release. 4 The selective GABAA-receptor antagonist bicuculline (3 and 100 microM) did not block the effect of GABA, while 3-amino-1-propanesulphonic acid (3-APA), a blocker of GABAB-receptors reversed the inhibitory effect of GABA. The results suggest that neuronal GABAB-receptors are involved in the GABA-evoked suppression of stimulated noradrenaline release.