DIRECT RENAL VASODILATATION PRODUCED BY DOPAMINE IN THE DOG

The effects on directly measured renal blood flow, mean blood pressure, and calculated renal vascular resistance of intravenous infusions of dopamine, isoproterenol, and norepinephrine were compared. Dopamine, at doses not affecting mean blood pressure, decreased renal vascular resistance and increased renal blood flow. In contrast, isoproterenol decreased both blood pressure and renal vascular resistance but did not consistently increase renal blood flow. Renal artery injection of dopamine produced vasodilatation at doses ranging from 0.75 to 12 µg and biphasic flow responses including transient vasoconstriction at higher doses. It is concluded that the probable basis for the effect of intravenous dopamine infusion on renal blood flow is its direct renal vasodilating action.

The direct effect of dopamine on the femoral vascular bed is vasoconstriction. The combination of renal vasodilating, and femoral vasoconstricting, effects is unique and is interpreted as evidence for a renal vasodilating effect of dopamine distinct from the conventional beta-adrenergic mechanism. A possible physiological role for dopamine other than as a precursor to norepinephrine may be related to this property. It is also suggested that the ability of dopamine to alter the distribution of cardiac output in favor of visceral organs may find useful clinical applications.

PRESSOR EFFECT OF RENIN

The pressor activity of renin administered intravenously at various rates and at various states of purity was measured and the effects of anesthesia, heparinization, and atropinization were investigated. Under all of these conditions, the blood pressure of normotensive and hypertensive dogs was elevated considerably throughout the period of infusion and for some time thereafter. The pressor activity of single doses of angiotensin and of renin was abolished and that of norepinephrine was inhibited, up to 85%, during the infusion of renin. The refractory state (socalled tachyphylaxis) to renin is not specific, since the continuous infusion of methoxamine likewise abolished the pressor activity of superimposed single doses of renin or angiotensin. At a very high rate of infusion, renin caused two exceptional and highly abnormal effects, the return of the blood pressure to the base line during the infusion, and the failure of the infused renin to inhibit the pressor action of single doses of norepinephrine.

CENTRAL CARDIOVASCULAR ACTIONS OF GAMMA-AMINOBUTYRIC ACID

The vasomotor and cardiac effects of gamma-aminobutyric acid (GABA) administered by different routes were studied in cats and dogs. The cat was resistant to the action of GABA administered intravenously or into a vertebral artery. Intrathecal injection of GABA into the cat depressed the vasomotor reponse to spinal compression. In dogs, intravenous, intrathecal or intraventricular injection, or topical application of GABA to the floor of 4th ventricle consistently produced hypotension and depressed the reflex and direct excitability of the vasomotor neurones, located at the supraspinal and spinal levels. Bradycardia observed after intravenous and intraventricular injections of GABA into dogs was abolished by stellate ganglionectomy but not by vagotomy. It has been attributed to depression of the central sympathetic neurones.

THE ACTION OF SODIUM 4-HYDROXYBUTYRATE ON SPINAL REFLEXES

The actions of sodium 4-hydroxybutyrate, gamma-aminobutyric acid and meprobamate have been studied in unanaesthetized animals, in local anaesthetic tests, on isolated organ preparations, on convulsions induced by picrotoxin and strychnine, and on monosynaptic (patellar) and polysynaptic (plantar) reflexes of the spinal cord. Sodium 4-hydroxybutyrate induced a sleep-like state with three unusual features: the righting reflex was remarkably persistent, respiration was good throughout and recovery was abrupt. gamma-Aminobutyric acid was inactive and meprobamate caused flaccid paralysis with loss of the righting reflex. None of the agents affected the responses of the rat diaphragm either to direct stimulation of the muscle or to indirect stimulation through the phrenic nerve. Only meprobamate reduced the responses of theguinea-pig isolated ileum preparation, showed local anaesthetic action and had an anticonvulsant action. All three compounds were capable, after intravenous or topical application, of blocking plantar reflexes in doses which did not affect the patellar reflex. The spinal animal responded in the same way, to the same dose of sodium 4-hydroxybutyrate, as the decerebrate preparation. Topical application to the motor cortex had no effect on spinal reflexes. We conclude that sodium 4-hydroxybutyrate acts preferentially on the internuncial neurones in the spinal cord but differs from meprobamate in its other actions. The similarity between the actions of sodium 4-hydroxybutyrate and of gamma-aminobutyric acid provides furtherevidence in support of the hypothesis that sodium 4-hydroxybutyrate is involved in the gamma-aminobutyric acid metabolic pathways.

CIRCULATING INTERFERON IN MICE AFTER INTRAVENOUS INJECTION OF VIRUS

Circulating interferon was detectable in mouse serum within 1 hour after the intravenous injection of various types of virus and it reached maximum levels in about 4 hours. Rapidly produced interferon may play a role in the pathogenesis of viral infection and in viral interference.

THE EFFECTS OF BETHANIDINE ON THE PERIPHERAL CIRCULATION IN MAN

Bethanidine has been administered intra-arterially and intravenously into normotensive subjects and its effects on the limb blood vessels, arterial blood pressure, vascular sensitivity to noradrenaline and the degree and time course of sympathetic nerve blockade have been studied. The drug caused an initial constriction of hand and forearm vessels which is attributed to release of catechol amines since it is abolished by the prior administration of phenoxybenzamine. The constriction was followed by a sustained vasodilatation lasting between 5 and 20 hr. Sympathetic blockade of hand vessels commenced immediately on infusion and was complete within 1 hr of administration. Recovery occurred in about 5 hr. Sensitivity to intra-arterial noradrenaline was increased within 10 to 15 min of infusion and before sympathetic blockade was complete. Intravenous administration caused a slight rise in blood pressure of supine subjects. Baroreceptor reflex responses of heart and of limb vessels elicited by tilting the subject feet downwards were abolished by bethanidine and postural hypotension occurred. Bethanidine is a potent sympathetic blocking agent in man with properties intermediate between those of bretylium and guanethidine.