Effects of cooling and rewarming on Na, K, and tension changes in rat tail artery

The relation of cell Na and K to vascular smooth muscle tension was studied in the isolated, perfused rat tail artery. Glass electrodes were used to measure ion exchanges; cooling and rewarming were used to modify cell ion content and exchange rates. The cells, made Na-rich and K-poor by overnight cooling of the artery at 2 °C, responded weakly to vasoactive agents (norepinephrine, L-8 vasopressin, and angiotensin) and characteristically showed a slow rate of rise followed by a still slower rate of fall in tension. Within minutes of initiating rewarming to 37 °C the rate of rise was accelerated even in the presence of metabolic inhibitors. The degree of rise depended on the degree of restoration of ionic gradients; it increased progressively with the time allowed for extrusion of Na and reaccumulation of K, a process which could be blocked by iodoacetate. During rewarming, the Na/K exchange rate rose from zero at 2 °C to reach a maximum toward the end of the first hour of rewarming, and in this interval the rate of relaxation following stimulation returned to normal. Stimulation of the cold artery with angiotensin enhanced subsequent Na outflow during rewarming without affecting K inflow, and the tissue was unable to respond to a second stimulus.

A Study of Erosion Between Two Parallel Surfaces Oscillating at Close Proximity in Liquids

A disk was vibrated in close proximity to a plane surface while submerged in either water or one of several oils. The specimens suffered surface damage either by subsurface fatigue or cavitation erosion. The type and extent of damage depends upon the thickness of the fluid films and the viscosity of the liquid. Specimens with bearing alloy surface layers showed cracks due to surface shear followed by flaking off of the bearing alloy.

Biphasic effects of graded doses of pitressin

Pitressin was administered subcutaneously at three dose levels (20 mu, 100 mu and 1000 mu) to rats made hypertensive with DCA. The excretion of Na, K and water was followed in each case during two consecutive collection periods of 4 hours each. These two periods were selected as corresponding to the pressor and depressor phases of Pitressin action, respectively. The selection of control and hypertensive animals was based on a preliminary blood pressure determination obtained by direct electromanometry from the femoral artery. At the low dose level of 20 mu a simple antidiuretic effect predominates and is apparent during the first collection period. At the intermediate dose level of 100 mu the simple antidiuresis is still evident during the first collection period. The second collection period is, however, marked by well defined Na retention with a lesser degree of water retention. The Na retention is not preceded by any antecedent Na loss. At the high dose level of 1000 mu the first period is distinguished as a phase of marked Na loss. In this phase the excretions of water and K are also increased but these appear to be only secondarily affected. The second period is again marked by well defined Na retention. These effects also occur in the normal animal given this dose of Pitressin. These experiments are taken to demonstrate that the biphasic effect of Pitressin on salt and water handling may be elicited in both the salt loaded and nonloaded rat. Attention is also drawn to the fact that there is a rough correlation between the effects of Pitressin on blood pressure and on salt and water metabolism.

Biphasic effect of pitressin on sodium tolerance in the hypertensive rat

The effect of a large dose of Pitressin (2 iu subcutaneously) on Na and water excretion under load was studied in rats made hypertensive by DCA. This dose is calculated to be within the upper limit of physiological secretion by the neurohypophysis. The excretion pattern was determined during the 4 1/2 hours following gavage with 100 mg of NaCl in 3 cc of water, both for the period immediately following Pitressin administration and for the period 3 hours after administration. These two periods were selected as corresponding to the pressor and depressor phases of Pitressin action, respectively. The procedure was carried out after one, four and eight daily injections of Pitressin. The selection of control and hypertensive animals was based on a preliminary blood pressure determination obtained by direct electromanometry from the femoral artery. The experiments demonstrated that Pitressin at this dose level has a biphasic action on the handling of Na and water as it has on blood pressure. The first phase consists of a limited tendency to accentuate the already accelerated rate of Na and water excretion found in the hypertensive state. This first effect was not obtained after eight injections. The second phase is characterized by a marked decrease in Na and water excretion which appears to be independent both of the antecedent rate of Na and water loss and of the number of injections.