Arginine vasopressin as a neurotransmitter in brain.

Arginine vasopressin (AVP) which exerts diverse biological effects in mammals is no more restricted to the posterior pituitary. Neurons containing AVP are seen in many other areas and in CNS vasopressinergic neurons are identified from the neocortex to the spinal cord. With the characterization of three different types of vasopressin receptor subtypes V1a, V1b and V2 responsible for its actions, their cloning and identification in different areas--especially in the brain many more hitherto unknown functions of AVP in brain has come to light. Added to this is the recently available specific vasopressin receptor antagonists. At present AVP seems to be involved in memory retrieval, learning, circadian time keeping, modulating the actions of area postrema and many other functions in brain. In the suprachiasmatic nuclei (SCN)--the biological clock--an area of the brain where the role of VP is still not very clear, VP is found to participate not only in transmitting the circadian rhythms to the rest of the brain but also serves the function of synchronizing and amplifying the pacemaker output of SCN. AVP can act not only as a neurotransmitter but also can stimulate the production of chemicals/neurotransmitters and thereby act as a mediator. It may be concluded that there is a central vasopressinergic system which participates in a variety of physiological and behavioral functions of brain.

Effect of vitamin D deficiency on electrocardiogram of rats.

Electrocardiograms (ECGs) were studied in rats fed vitamin D deficient diet for 12 weeks. The results indicated significant shortening of QT interval of ECG. Other intervals were normal when compared with age matched control rats. Heart/body weight ratio was significantly increased in vitamin D deficient group, which is an index of hypertrophy, with increased collagen fiber in the histology of the myocardium, inspite of normal serum calcium level. The results suggested a direct role of vitamin D in the regulation of cardiac functions.

Circanual variation of sperm count and motility in men.

Seasonal variation in rhythmicity of spermatogenesis might be due to external temperature fluctuation which could partially be responsible for decreased sperm counts in summer. Other factor like exposure to light might contribute for the reduction in sperm counts. These facts should be taken into account before diagnosing male fertility.

Effect of graded doses of naloxone on renal function in canine hemorrhagic shock.

All the parameters of renal function (inulin clearance, para amino hippuric acid clearance and urine flow) which were depressed during experimentally induced hemorrhagic shock in dogs improved significantly in addition to improvement in mean arterial pressure (MAP) after bolus administration (iv) of 1 or 2 mg/kg naloxone. A smaller dose (0.5 mg/kg) of naloxone, however, did not improve the renal function. Even renal arterial injection of the same dose of naloxone showed no improvement in the renal function. In both these cases the improvement in the MAP was significantly less as compared to other groups of animals which received 1 or 2 mg/kg naloxone. It may be concluded that (a) naloxone at doses of 1 or 2 mg/kg improved the renal function by improving MAP and (b) naloxone has no direct action on renal vasculature.

Effect of naloxone on renal cortical microcirculation in haemorrhagic shock.

In order to assess the effect of opioid receptor antagonists, naloxone and noradrenaline, on renal cortical microcirculation, India ink infusion was made through the renal artery, one hour after treatment with each drug, in dogs subjected to haemorrhagic shock. Naloxone (1 mg/kg) treatment showed a dual beneficial effect of significant improvement (P < 0·001) in the mean arterial pressure without increasing the renal resistance as indicated by the presence of ink particles in about 75% of the cortical glomeruli. However, in the case of noradrenaline (2 μg/kg/min)-treated animals, although mean arterial pressure increased significantly (P < 0·001) only very few glomeruli (25%) in the cortical region showed ink particles, demonstrating severe vasoconstriction. In the control group infused only with saline, although most of the glomeruli (92%) were filled with ink particles, there was a significant decline in the mean arterial pressure (P < 0·001).

Comparison of effects of naloxone and catecholamines on acid-base balance in canine hemorrhagic shock.

The present study was conducted to compare the effect of naloxone, an opiate receptor antagonist, with catecholamines on acid-base status and survival in dogs subjected to hemorrhagic shock. Arterial lactic acid concentration which had increased during hemorrhage, decreased significantly (P less than 0.05) in naloxone treated animals but increased further in catecholamine treated dogs. Blood bicarbonate concentration and PCO2 which had markedly decreased 1 hr after hemorrhage recovered significantly (P less than 0.05) in naloxone group of animals. On the other hand bicarbonate and pH declined further in noradrenaline group and remained unchanged in dopamine group. These results as well as better survival rate observed in naloxone treated animals suggest the superiority of naloxone over dopamine and noradrenaline, as an adjunct to blood transfusion in the treatment of hemorrhagic shock.

Amygdalar injections of vasopressin and its antagonist do not disrupt the circadian rhythm of food and water intake in the rat.

There is an indication that areas of the brain other than the suprachiasmatic nuclei (SCN), the known neural circadian pacemaker, are involved in the control of circadian rhythms. The present study investigated the role of amygdala in the circadian rhythms of food and water intake. Vasopressin and its antagonist d(CH2)5Tyr(Me)AVP were injected into the amygdala bilaterally through chronically implanted stainless steel cannulae. The results of the study have shown that neither vasopressin nor its antagonist d(CH2)5Tyr(Me)AVP alters the circadian rhythm of food and water intake thereby showing that vasopressinergic neurons/projections to amygdala are not involved in the control of circadian rhythms of food and water intake and amygdala is not likely to be an additional oscillator.