The American journal of physiology
-
We studied the cardiovascular effects of altering GABA-ergic tone in the posterior hypothalamus in rats. Animals were equipped with chronic guide cannulas placed in the posterior hypothalamus, arterial and venous catheters, and a bipolar electrode on the splanchnic nerve. ⋯ In contrast, muscimol infused into the posterior hypothalamus of anesthetized rats failed to alter heart rate or blood pressure. We conclude that 1) the posterior hypothalamus contains a sympathoexcitatory system that is modulated by changes in GABA-ergic tone and 2) tonic GABA-ergic inhibition is sufficient to completely suppress the activity of this hypothalamic sympathoexcitatory system in anesthetized animals but not in conscious rats.
-
We tested the hypothesis that hypoxic hypoxia interferes with cerebral blood flow (CBF) autoregulation when intracranial pressure (ICP) is elevated in pentobarbital-anesthetized lambs (3 to 9 days old). Cerebral perfusion pressure (CPP) was lowered stepwise from 73 to 23 mmHg in eight normoxic lambs and from 65 to 31 mmHg in eight other hypoxic lambs by ventricular infusion of artificial cerebrospinal fluid. In normoxic lambs, CBF measured by microspheres was not significantly changed over this range of CPP. ⋯ Cerebral O2 uptake was similar in both groups and did not decrease when CPP was reduced. These results demonstrate that normoxic lambs have a considerable capacity for effective autoregulation of CBF when ICP is elevated. Moreover, cerebral vasodilation in response to a level of hypoxia approximating that normally seen prenatally does not abolish CBF autoregulation when ICP is elevated during the first postnatal week.
-
The influence of acidosis on the inotropic effect of isoproterenol was studied in the isolated arterially perfused heart of the newborn rabbits. Baseline mechanical function during acidosis (pH 6.8) was not different from control (pH 7.4). However, the inotropic effect of isoproterenol was significantly suppressed in the acidotic muscles. ⋯ Adenylate cyclase activity was depressed at pH 6.8 and 6.0. These data suggest that the inotropic effect of isoproterenol is diminished in the acidotic muscle. This may be due to the decreased activation of cAMP production, which in turn most likely results from depressed adenylate cyclase activity.
-
Although endogenous opioids have been implicated in the pathophysiology of spinal cord injury and brain ischemia, the role of specific opioid peptides and opiate receptors in the pathophysiology of traumatic brain injury remains unexplored. This study examined regional changes in brain opioid immunoreactivity and cerebral blood flow (CBF) after fluid-percussion brain injury in the cat and compared the effect of an opiate antagonist (Win 44,441-3 [Win-(-)]) with its dextroisomer Win 44,441-2 [Win-(+)] (which is inactive at opiate receptors) in the treatment of brain injury. ⋯ Win-(-) also significantly improved survival after brain injury. Taken together, these findings suggest that dynorphin, through actions at opiate receptors, may contribute to the pathophysiology of secondary brain injury after head trauma and indicate that selective opiate-receptor antagonists may be useful in treatment of traumatic brain injury.
-
Severe hemorrhage in pentobarbital-anesthetized dogs (25 mg/kg) is reversed by intravenous NaCl (4 ml/kg, 2,400 mosmol/l, 98% long-term survival). This paper compares survival rates and hemodynamic and metabolic effects of hypertonic NaCl with sodium salts (acetate, bicarbonate, and nitrate), chlorides [lithium and tris(hydroxymethyl)aminomethane (Tris)], and nonelectrolytes (glucose, mannitol, and urea) after severe hemorrhage (44.5 +/- 2.3 ml/kg blood loss). ⋯ Plasma sodium, plasma bicarbonate, mean circulatory filling pressure, cardiac output, and arterial pressure correlated significantly with survival; other parameters, including plasma volume expansion or plasma osmolarity, did not. It is proposed that high plasma sodium is essential for survival.