Effects of changes in circulating volume and in arterial pressure on plasma renin activity in the intact rat

The effects of changes in arterial pressure and in circulating volume on Plasma Renin Activity (PRA) in the intact rat were compared by two experimental procedures. Gradual volume depletion was induced by intraperitoneal injection of a hyperoncotic polyethyleneglycol solution (PEG) in absence of acute changes in Systolic Arterial Pressure (SAP). SAP was measured in the conscious state by the tail cuff technique. Plasma Protein Concentration (PPC) and Hematocrit (Hct) increases after PEG injection were compared as the index for measuring the Plasma Volume Reduction (PVR). PRA showed a significant (p less than 0.001) linear relationship with PPC, suggesting a direct dependence of renin secretion on volume depletion. Acute changes in the circulating volume were induced by controlled hemorrhages of 5.0, 10.0, 15.0 and 20.0 ml of blood/kg body weight. The increase in PRA showed a significant relationship with the changes in circulating volume, but it did not show any dependence on the changes in Mean Arterial Pressure (MAP). Our results suggest that, in the intact and conscious rat, renin secretion responds to the information from the cardiopulmonary volume receptors rather than to that from the high pressure receptors.     

Prevalence and identity of coccidia in pen-raised wild turkeys

One hundred nineteen pen-raised wild turkeys (Meleagris gallopavo) from 12 locations in nine states in the United States were examined for coccidia by sugar flotation of intestinal contents and mucosa or by subinoculating the contents into uninfected domestic turkeys. Seventy-eight (66%) of the turkeys were positive for coccidia. There were no differences in the frequency of coccidia among adult, sub-adult or juvenile turkeys. More females (75%) were infected than males (48%). The species of coccidia from 30 of the turkeys were identified based on microscopic examination of oocysts, fresh scrapings, stained sections and inoculations of bobwhites (Colinus virginianus). The frequency of each species was Eimeria meleagrimitis (97%), E. gallopavonis (47%), E. meleagridis (27%), E. dispersa (17%), E. innocua-E. subrotunda (13%), E. adenoeides (7%) and an undescribed species (3%). Of the 30 turkeys in which the species of coccidia was determined, 30% had a single species infection, 40% had two species, 20% had three species and 10% had four species.     

Single chloride channels in cultured rat neurones

Single-channel currents through chloride channels were recorded in cultured hippocampal neurones from rats using the patch-clamp method. The channel is active at voltages between -80 and +80 mV, and the time spent in the open state increases with depolarization (almost fourfold for 120 mV). The channel conductance is 62 pS in symmetrical 150 mM NaCl saline. In salt gradient conditions the channel was measurably permeable to Na+. Substitution of NO3- and Br- for Cl- gave higher single-channel currents, meaning a higher permeability of the channel toward the two anions than to Cl-. SO4(2-) ions were poorer charge carriers, yet contributed measurable inward current at negative voltages. Channel activity appeared independent of intracellular Ca2+ concentration. Taken together, these features would suggest for this channel a role in stabilizing resting membrane potential and in maintaining normal cell excitability.     

Prostaglandin I2 is less relaxant than prostaglandin E2 on the lamb ductus arteriosus.

Prostaglandin (PG) I2 and its stable metabolite, 6-keto-PGF1alpha, were tested on the isolated ductus arteriosus from mature fetal lambs. PGI2 relaxed the ductus in high doses (threshold 10(-6)M) and its activity disappeared on standing at room temperature for 30 minutes. 6-keto-PGF1alpha was inactive at all doses. By contrast, PGE2 produced a dose-dependent relaxation over a range between 10(-10) and 10(-6)M. These findings confirm that PGE2 is the most potent ductal relaxant among the known derivatives of arachidonic acid. PGE2 probably maintains ductus patency in the fetus and, together with PGE1, remains the compound of choice in the management of newborns requiring a viable ductus for survival.     

Overnight dexamethasone suppression test: normal responses and the diagnosis of Cushing's syndrome

Serum cortisol levels were measured the morning after the administration of 1 mg of dexamethasone. Only 5 of 190 subjects had serum cortisol levels greater than 2 micrograms/dL. Thus, the normal value after dexamethasone suppression is less than 2 micrograms/dL rather than less than 5 micrograms/dL as has generally been accepted. The distinction is important because some individuals with Cushing's syndrome partially suppress their cortisol levels to less than 5 but more than 2 micrograms/dL during the test procedure. Thus, the use of 5 micrograms/dL as the normal value may lead to an unnecessary delay in diagnosis.