ACUTE AND CHRONIC EFFECTS OF THE INSECTICIDE ENDRIN ON RENAL FUNCTION AND RENAL HEMODYNAMICS

Variable effects of chlorinated hydrocarbon insecticides on the kidney have been reported. The purpose of the present study was to determine the acute and chronic effects of the insecticide endrin on renal function and hemodynamics in dogs. Dogs were exposed to endrin acutely by intravenous infusion, and chronically by intramuscular injection. In acute experiments, dogs developed systemic hypertension and increased renal vascular resistance attributable to a sympatho-adrenal action. Acute effects of endrin were predominantly afferent arteriolar vasoconstriction as evidenced by decreases in renal blood flow, glomerular filtration rate, and urine flow. Phentolamine and phenoxybenzamine increased renal blood flow after endrin, providing evidence for humorally induced renal vasoconstriction due to adrenergic agents. Adrenalectomy partially offset the marked drop in renal blood flow after endrin although systemic hypertension and bradycardia were unaffected. Results from renal denervation experiments were variable. Changes in renal function in chronic studies were minimal and appeared to be due to secondary alterations in systemic hemodynamics. Results from this investigation provide no evidence for renal failure attributable to the direct effects of endrin.

HEART RATE RESPONSES TO APNEIC UNDERWATER DIVING AND TO BREATH HOLDING IN MAN

Bradycardia is a response to apneic diving which man has in common with many other species. Slowing of the heart rate during diving was observed in children as well as adults and was as prominent in poor swimmers as in those subjects who were familiar with the water. The response was independent of depth down to 27 m, but could not be produced by simulated dives in a compression chamber. Diving in water implies several maneuvers, some of which were investigated during breath holding. It was observed that the tachycardia produced by breath holding at different Valsalva pressures was proportional to the increase of intrathoracic pressure. At equal pressures the tachycardia was less when the subject was in water than when in air. Other maneuvers which increased venous return at the beginning of the breath hold produced a bradycardia during the apnea, and conversely when venous return was impaired there was a tachycardia. The hypothesis is presented that diving bradycardia in man might be explainable in terms of already known physiological mechanisms.

swimming; submersion

Submitted on February 27, 1963

CAROTID SINUS DEPRESSOR REFLEXES DURING HYPOTHERMIA

Reducing body temperature in dogs to 24 C caused a small reduction in the size of the carotid sinus depressor response. Along with this reduction the response also became more gradual at the lower body temperatures. Systematic studies demonstrated that the more gradual nature of the response appeared to result from changes in the vascular smooth muscle. Depression of the nervous elements of the baroreceptor reflex arc during hypothermia was not evident. The response to carotid sinus stimulation in the warm, perfused hindlimb was essentially unchanged by cooling the body to 24 C. Local cooling of the perfused hindleg did not reduce the size but did result in a more gradual response.

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.

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.

A COMPARISON OF IMIPRAMINE, CHLORPROMAZINE AND RELATED DRUGS IN VARIOUS TESTS INVOLVING AUTONOMIC FUNCTIONS AND ANTAGONISM OF RESERPINE

Seven structurally-related compounds consisting of three antidepressant drugs (imipramine, desmethylimipramine and amitriptyline), three tranquillizing agents (promazine, chlorpromazine and chlorprothixene) and a hybrid, desmethylpromazine, have been examined in a series of tests involving autonomic functions and antagonism of reserpine. Activities of the compounds in antagonizing reserpine-induced ptosis in rabbits and prolongation of alcohol hypnosis in mice give good correlation with their clinical actions, whilst their activities in augmenting excitation of rats by amphetamine and yohimbine toxicity in mice, and in reversing reserpine-induced bradycardia in rats offer further evidence for drug-induced sensitization to adrenergic or tryptaminic mechanisms, which is not however specific for antidepressant agents. No evidence has been obtained to indicate that a central parasympatholytic action is an important component of the antidepressant activity of imipramine and related drugs.