[1-Desaminopenicillamine, 8-alpha-hydroxyisocaproic acid] oxytocin. A selective inhibitor in rats of the uterine response to oxytocin

Pharmacological characteristics and anatomical distribution of [3H]oxytocin-binding sites in the Wistar rat brain studied by autoradiography

Oxytocin-binding sites were detected by autoradiography on rat brain sections incubated in the presence of the [3H]oxytocin. These sites were characterized pharmacologically using quantitative autoradiography. High pressure liquid chromatography controls of the incubation media indicated that labelling was due to the intact [3H]oxytocin molecule. Pharmacological analysis of different locations (central amygdaloid nucleus, ventral subiculum and ventromedial hypothalamic nucleus) showed that the sites detected had a high affinity for oxytocin and also for arginine-vasopressin. In contrast, some areas known to bind vasopressin intensely, such as suprachiasmatic and lateral septum nuclei, had little or no affinity for oxytocin. Autoradiographs revealed [3H]oxytocin-binding sites in already known brain areas (olfactory centres, ventral subiculum, central amygdaloid nucleus, bed nucleus of the stria terminalis) albeit with more extensive labelling of some of these formations, in particular, the amygdaloid complex. In addition, specific [3H]oxytocin-binding sites were found in areas not yet reported to bind oxytocin, such as the paraventricular thalamic and caudate nuclei. In the hypothalamus, specific binding sites were not detected in the supraoptic and paraventricular nuclei: the only structure labelled was the ventrolateral part of the ventromedial nucleus. Discrepancies between the concentrations of [3H]oxytocin-binding sites, the known distribution of oxytocin-containing endings and electrophysiological data indicate that autoradiography, under our conditions, apparently only reveals some of the oxytocin receptors in the brain. Thus, in the hypothalamus, no relationship can be established between the known effect of oxytocin on oxytocinergic magnocellular neurons and detection of specific [3H]oxytocin-binding sites. Autoradiography may reveal mainly oxytocin-binding sites in areas receiving diverse "parasynaptic" information, where oxytocin might play a modulatory role rather than exerting rapid, short-term effects of the neurotransmitter type.

Desaminopenicillamine tocinoic acid derivatives--inhibitors of oxytocin

Tocinoic acid analogs with penicillamine in place of one or both of the cysteine residues have been studied and [1-beta-mercaptopropionic acid, 6-penicillamine] tocinoic acid (dPen6TA) and [1-beta,beta-dimethyl-beta-mercaptopropionic acid, 6-penicillamine] tocinoic acid (dPen1Pen6TA) have been synthesized in solution. Biological activities of these 2 compounds and those of the previously synthesized [1-beta,beta-dimethyl-beta-mercaptopropionic acid] tocinoic acid (dPen1TA) have been assayed. It was found that dPen1TA and dPen1Pen6TA, both of which have a beta,beta-dimethyl-beta-mercaptopropionic acid in position 1, are strong inhibitors of the uterine activity of oxytocin in vitro (without Mg2+) with pA2 values of 7.1 and 7.8, respectively, whereas dPen6TA with penicillamine in position 6 is a mild agonist.