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.

Pulse wave velocity and lipid profile in varicose vein patients.

In 20 varicose vein patients, aged twenty-five to forty-five years, and suffering the disease for more than two years, pulse wave velocity (PWV) of the femoral-dorsalis pedis artery of the lower limbs was measured and compared with that of 20 age-matched normal subjects. Blood pressure and fasting serum total cholesterol level, triglycerides, high density lipoprotein (HDL), low density lipoprotein (LDL), very low density lipoprotein (VLDL) were also estimated for these subjects. PWV showed a significant increase (P < 0.001) in varicose vein patients as compared with control subjects. There was no significant difference either in the blood pressure or lipid profile. It appears that neither hypertension nor atherosclerosis is responsible for the increase in PWV in varicosities. On the basis of the present study, it may be suggested that arteries are also involved in the pathogenesis of varicose veins. The involvement of the arterial tree in the pathogenesis of varicose veins, if given due consideration, may add a new dimension to the understanding of many ill-defined facets of this disease.

Effect of vitamin D repletion on testicular function in vitamin D-deficient rats.

Freshly weaned 30-day-old male Wistar rats were fed a vitamin D-deficient diet adequate in calcium and phosphorus for 3 months. On the 120th day of age three different doses of vitamin D were injected intramuscularly into three groups of rats and maintained for another month with water and a normal diet ad libitum. One group was continued with a vitamin D-deficient diet up to the 150th day. One group of animals was killed by decapitation on the 120th day and testicular functions like sperm count in testis and epididymis, testicular glutamyl transpeptidase activity and Leydig cell count as well as body weight were noted. On the 150th day animals of all groups were killed and testicular function was studied. Body weight and testicular function decreased significantly on the 120th and 150th day of age in vitamin D-deficient rats as compared to age-matched normal control rats. Injection of lower doses of vitamin D on the 120th day of age improved testicular function after 1 month whereas administration of a high dose of vitamin D caused a deterioration of the testicular function. The result suggests that retardation of spermatogenesis due to disturbances in Sertoli and Leydig cell function in vitamin D deficiency is reversible and can be corrected by supplementing an optimal dose of vitamin D.

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.

Vasopressin antagonist disrupts the circadian rhythm of water intake on suprachiasmatic injection.

The present study makes an attempt to find out the action of arginine vasopressin (AVP) and its antagonist d-(CH2)5 Tyr (Me) AVP applied at the suprachiasmatic nuclei (SCN) on the circadian rhythm of water intake. Chronic implantation of a 22 G stainless steel cannula for injection was performed using a stereotaxic technique under Nembutal anesthesia. AVP and its antagonist were injected into the SCN of free-moving rats at the beginning of light and dark phases of the light-dark (LD) cycle. Injections of AVP during either phase did not disrupt the circadian pattern of water intake while the injections of the antagonist disrupted it. The findings are suggestive of the involvement of AVP as a mediator of the circadian rhythm of water intake at the level of the neural pacemaker, SCN.

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 vitamin D deficiency on testicular function in the rat.

To study the effect of vitamin D deficiency on testicular function, 30-day-old male rats were put on a vitamin-D-deficient diet. At 120 days of age, the testicular function of these animals was compared with that of rats of the same age group fed, ad libitum, a diet containing vitamin D and rats fed on a restricted amount of diet with vitamin D. In vitamin-D-deficient rats, there was a significant reduction in the total body weight, testicular and epididymal sperm count and testicular glutamyl transpeptidase activity (an index of Sertoli cell function) as compared to control group rats, but there was no difference in the testicular lactate dehydrogenase activity (an index of germ cell function). Histological examination of the testis in vitamin-D-deficient rats revealed a significant reduction in the Leydig cell count along with degenerative changes in the germinal epithelium. Histological examination of the tibia revealed excess of osteoid in vitamin-D-deficient rats only. On the other hand, in undernourished rats given a normal amount of vitamin D, the only significant change was a reduction in total body weight. These results suggest that vitamin D deficiency retards spermatogenesis by interfering with the function of Sertoli and Leydig cells.

Vasopressin: its possible role in circadian time keeping.

In this review article an insight has been made into the strong possibility of the role of vasopressin (VP) in the control of circadian rhythms which has emerged from the results of the recent experiments in this field. A role for VP, which is identified in the suprachiasmatic nuclei (SCN) of mammals, as a neurotransmitter/neuromodulator in the central nervous system has been postulated for some time now. The presence of certain abnormalities in the circadian rhythms in VP deficient Brattleboro rats has suggested that this neuropeptide is a likely candidate in controlling circadian rhythms. The coexistence of VP and corticotropin releasing factor (CRF), their interrelation with reference to their role in the hypothalamus-pituitary-adrenocortical glucocorticoid axis not only in states of stress but also in day-to-day life has also been discussed. The possible role of dynorphin, which is co-synthesized with VP in the hypothalamic neurons, and other opioids in the control of circadian rhythms has been highlighted. The pineal, SCN relation in the process of development of circadian rhythms has also been reviewed briefly.

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.

Lithium chloride SCN injection alters the circadian rhythm of food intake.

Effect of lithium injections through chronically implanted cannulae into the bilateral suprachiasmatic nuclei (SCN) on the circadian rhythm of food intake was investigated in the rat. It was observed that the circadian rhythm was disrupted by injections of lithium at the beginning of the light as well as the dark phase of the LD cycle. In either case the percentage of the food consumed during the 12-hr light period increased while that during the dark period decreased without any significant change in the total daily intake. Disruptions in the circadian rhythm of food intake failed to show any dose-response relation. Injections of saline into the SCN or lithium into the nearby SCN area did not produce a disruption of the circadian rhythm of food intake.

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.