The hypothalamic neurosecretory pathways for the release of oxytocin and vasopressin in the cat

Abstract

SUMMARY1. The neurones of the supraoptic nucleus (SON) and paraventricular nucleus (PVN) were stimulated electrically in lactating cats under chloralose anaesthesia. Milk-ejection responses were used to monitor the release of oxytocin and vasopressin and both hormones were assayed in samples of blood collected during stimulation. The position of the tip of the stimulating electrode was confirmed from brain sections stained selectively for cystine-rich neurosecretory material.2. A previous finding that stimulation of the SON in the cat releases vasopressin without oxytocin was confirmed.3. Stimulation of the PVN caused both hormones to be released. The ratio of their concentrations in blood was variable; this suggests release from separate neurones.4. Both hormones were also released on stimulation of the median eminence but not ofthe zone lying vertically between this structure and the PVN. No neurosecretory material was detected in this zone. These findings argue against the existence of a direct or medial paraventriculo-hypophysial pathway running downwards along the wall of the third ventricle.5. Study of sections from unstimulated brains confirmed that the tractus paraventricularis cinereus of Greving which runs ventro-laterally from the PVN towards the SON, represents the principal efferent pathway for neurosecretory fibres from the PVN.6. The results are discussed in relation to the problem of the independent release of oxytocin and vasopressin in response to physiological stimulation of the neurohypophysis.

Vasopressin Release by Nicotine: The Site of Action

“…Blood pressure was recorded from a femoral artery with a Statham strain gauge transducer and a Goertz potentiometric recorder (1 mmHg = 1.33 mbar). The same method of recording was used for determining the milkejection pressure from a cannulated teat duct in lactating cats in order to monitor the release of neurohypophysial hormones as described by Bisset, et al ( 1971).…”

“…In order to prevent inhibition of the milkejection response by any adrenaline or noradrenaline that might be released into the circulation by nicotine, oxprenolol hydrochloride (Trasicor, Ciba) (4 mg) was injected intravenously because this ,B-adrenoceptor blocking agent has been shown to prevent inhibition of the milkejection response produced by adrenaline (Bisset, Clark & Lewis, 1967;Bisset et al, 1971). Oxprenolol was given routinely also to the non-lactating cats to maintain the same experimental conditions.…”

“…The extracts were assayed for vasopressin by their antidiuretic activity on intravenous injection into water-loaded rats under ethanol anaesthesia, and for oxytocin by their milk-ejecting activity on retrograde arterial injection into lactating rats treated with oxprenolol. These assay methods have been described in detail by Bisset et al (1971). The standards used for the assay were synthetic arginine-vasopressin (Sandoz) and synthetic oxytocin (Syntocinon, Sandoz).…”

“…In the assay for oxytocin, interference from the intrinsic milk-ejecting activity of vasopressin (Bisset et al, 1971) was avoided by treating the extracts with trypsin before assaying them for milk-ejecting activity. Trypsin is known to inactivate vasopressin in brain extracts without affecting oxytocin (Bisset, Errington & Richards, 1973).…”

“…1969 hand, in the cat, electrical stimulation of the PVN increases the concentration of both hormones in the blood (Bisset, Clark & Errington, 1971).…”