THE EFFECT OF SOME PHENOTHIAZINE TRANQUILLIZERS ON THE OESTROUS CYCLE OF ALBINO MICE

The effects of reserpine and of nine phenothiazine compounds on the oestrous cycle of albino mice were tested. With the exception of promethazine (which is not a tranquillizer) all the phenothiazine compounds and reserpine prolonged the oestrous cycle. The mechanism by which these tranquillizers interfere with the oestrous cycle is discussed.

CIRCADIAN RHYTHM IN PINEAL SEROTONIN: EFFECT OF MONOAMINE OXIDASE INHIBITION AND RESERPINE

The pineal gland of the rat shows a circadian rhythm in its serotonin content, the amount of serotonin decreasing at night. This decrease can be prevented by inhibiting the action of monoamine oxidase. Reserpine abolishes the circadian rhythm in pineal serotonin in the same manner as does interruption of the sympathetic nervous connections of the central nervous system and the pineal gland. These observations suggest that circadian changes in release and binding of serotonin may occur in the pineal gland, and that a central mechanism in which monoamines participate may control the circadian pineal-serotonin rhythm.

EFFECTS OF SMALL ORAL DOSES OF RESERPINE ON VASCULAR RESPONSES TO TYRAMINE AND NOREPINEPHRINE IN MAN

Experiments were done to see if reserpine, in small oral doses, alters the responses to tyramine and norepinephrine in man. Each of seven normotensive subjects was studied on three occasions. The first and third sessions served as pre- and post-treatment control sessions; the second session was held after oral administration of reserpine (0.25 to 1 mg. per day) for 2 weeks. Blood pressure was measured with a sphygmomanometer, and forearm blood flow was measured with a water plethysmograph. Reserpine reduced resting blood pressure and heart rate but forearm blood flow did not change. The pressor, forearm vasoconstrictor, and bradycrotic actions of intravenous tyramine were suppressed by reserpine, but the pressor, vasoconstrictor, and bradycrotic actions of three intravenous doses of norepinephrine were not augmented significantly. The results indicate that oral administration of small doses of reserpine may cause depletion of endogenous catecholamines in man as suggested by the suppressed response to tyramine. The decreased response to tyramine was not accompanied by hypersensitivity to exogenous norepinephrine. In equipressor doses norepinephrine produced greater forearm vasoconstriction and more reflex bradycardia than did tyramine.

SOME OBSERVATIONS ON THE PHARMACOLOGY OF ALPHA-METHYLDOPA

alpha-Methyldopa in high concentrations impaired the responses of rabbit isolated ileum and guinea-pig isolated vas deferens to stimulation of the sympathetic nerves and to noradrenaline, but these preparations taken from animals previously treated with alpha-methyldopa showed no sign of impairment. Contractions of the cat nictitating membrane were reduced but not abolished by alpha-methyldopa. In cats, dogs and rats, pressor responses to noradrenaline were usually slightly increased by alpha-methyldopa. Pressor responses to tyramine were not affected consistently. alpha-Methyldopa, alpha-methyldopamine and alpha-methylnoradrenaline behaved like dopa, dopamine and noradrenaline respectively in restoring the responses of tissues from reserpine-treated animals to stimulation of the sympathetic nerves to the rabbit ileum, the guinea-pig vas deferens and the cat nictitating membrane and in restoring responses to tyramine of the cat blood pressure and nictitating membrane, and the rat blood pressure. The potency of alpha-methylnoradrenaline relative to noradrenaline ranged from one-half to one-ninth on various preparations. The results are discussed in relation to the antihypertensive action of alpha-methyldopa.

VENOUS AND ARTERIAL RESPONSES TO NOREPINEPHRINE IN DOGS TREATED WITH RESERPINE

Experiments were done to see if the effects of norepinephrine upon veins, arteries, and small vessels are augmented in dogs after treatment with reserpine. With intra-arterial injection of increasing doses of norepinephrine into the perfused foreleg there were progressive increments in total, arterial, small vessel, and venous resistances. In animals treated with reserpine the increments in total and small vessel resistances were greatly augmented while increments in segmental arterial resistance were increased only slightly. The venous responses in these treated dogs were not augmented. Similar effects on segmental resistances were noted with infusion of norepinephrine into a systemic vein. The vasoconstrictor effect of tyramine was reduced in treated dogs and was restored after intra-arterial and intravenous norepinephrine. The results indicate that veins do not participate in the increased vascular responsiveness to norepinephrine which occurs in forelegs of dogs after treatment with reserpine.

THE INFLAMMATORY RESPONSE TO IMPLANTATION OF COTTON PELLETS IN THE RAT

The subcutaneous implantation of a cotton pellet in the rat evokes a short-lasting phase of increased capillary permeability lasting some 20 min. after implantation followed by a more sustained phase which occurs after 2·5–3 hr. The early increase is antagonised by lysergic acid diethylamide, reserpine and 5-HT. The peak granuloma weight is reached at 2 days, and then falls rapidly. Antagonism of oedema and granulation tissue by hydrocortisone and reserpine can be demonstrated at 2 days after implantation.

MECHANISM FOR CARDIAC STIMULATION DURING HYPOXIA

In isolated guinea pig atria, hypoxia was induced by bubbling nitrogen through Tyrode solution. A significant increase in both the amplitude and frequency of the contractions occurred, followed by a decrease. Average rate in 11 control atria was 138 ± 9.2 contractions/min and increased during hypoxia by an average value of 12.7 ± 2.3 contractions/min ( P < 0.001). Amplitude of shortening increased by an average of 10.5 ± 2.12% ( P <0.001). In 19 preparations pretreatment with reserpine blocked the transient stimulant effect of hypoxia on both amplitude and frequency of contractions. Isometric contractions were recorded from 30 isolated cat papillary muscles. The developed isometric tension increased during hypoxia by an average of 17.3 ± 2.8% ( P < 0.001). Later, a decrease in contractile force was observed. Pretreatment of the animals with guanethidine and chronic cardiac sympathectomy blocked and pretreatment with reserpine decreased the stimulant effect of hypoxia on the cat papillary muscle. The transient stimulant effect of hypoxia was compared to the staircase phenomenon. Both chronic cardiac sympathectomy and pretreatment with reserpine blocked the increase in force induced by a change in rate from 60 to 120.