No abstract

No abstract

No abstract

Rabbit basilar artery rings are normally relatively unresponsive to transmural stimulation of their sympathetic nerve supply. However, in the presence of histamine (0.55 /i M )> contractile responses to nerve stimulation were markedly increased. Norepinephrine and serotonin concentrations that produce 50% of a maximum contractile response (ED 50 ) were considerably decreased in the presence of histamine; maximum responses to both norepinephrine and serotonin were increased. Although a prejunctional effect of histamine has not been eliminated, potentiation of responses to transmural nerve stimulation is probably due to an increase in smooth muscle responsiveness to norepinephrine. In rabbit saphenous artery rings, histamine produced a qualitatively similar potentiation of responses to nerve stimulation, norepinephrine, and serotonin except that maximum responses were not increased. Serotonin (0.084 JJM) did not potentiate contractile responses of the basilar artery to transmural nerve stimulation or norepinephrine. Since histamine and serotonin are released from rabbit platelets in response to tissue injury, the synergistic effect of these agents on vascular smooth muscle contraction might be advantageous in minimizing hemorrhage. But such a response could also be deleterious if the effects of these vasoconstrictors were prolonged. KEY WORDSnorepinephrine serotonin cerebral vasospasm hemorrhage nervous control of cerebral circulation saphenous artery basilar artery• Numerous studies of the physiology and pharmacology of the cerebral vasculature have been reported, yet controversy over the control of brain blood flow continues (1). This is especially true of nervous control of the cerebral circulation. Although an adequate sympathetic nerve supply to the larger cerebral arteries has been demonstrated by morphological techniques (2-4), its functional significance is still in doubt. Carefully designed studies in dogs have shown a decrease in cerebral blood flow with adrenergic nerve stimulation, although the high rates of stimulation which are necessary to elicit measurable changes cast some doubt on the relevance of this finding (5). Cerebral arteries have a low sensitivity to lnorepinephrine in comparison with that of other vessels (6, 7). Although cerebral arteries contract in vitro when their intramural nerves are stimulated electrically, this response is small in comparison This investigation was supported by U. S. Public Health Service Grant HL15805 from the National Heart and Lung Institute and by Grant 408 IG from the Los Angeles County Heart Association. Dr. Duckies is a Los Angeles County Heart Association postdoctoral fellow, and Dr. Lee is a U. S. Public Health Service postdoctoral fellow supported by Grant NS 2040. Received October, 15, 1974. Accepted for publication February 27, 1975. with that of other vessels (8); moreover, some workers have been unable to demonstrate a response in some species (7).Because of the uncertainty about nervous control of the cerebral circulation, we were inter...

The mechanism by which secondary porosity in sandstone reservoirs is produced is poorly understood. Previous hypotheses to account for the increased dissolution of framework silicates have invoked the introduction of acidic and/or organic-rich fluids capable of complexing metals. In order to evaluate the relative effects of these factors, the rates of K-feldspar dissolution have been measured at 70 ~ and 95 ~ at pH values of 1, 4, and 9, with and without oxalic acid, at a total pressure of 50 MPa, using direct sampling autoclaves. The presence of oxalic acid increased the dissolution rate of Kfeldspar at pH 4 and 9, but decreased the rate at pH 1 at both temperatures. The maximum increase in dissolution rate was observed at pH 4, 95 ~ by a factor -4. In oxalic-free experiments, the rate of dissolution increased an order of magnitude with each unit decrease in pH in the pH regime 1--4. In the presence of oxalic acid, this dependency of dissolution upon pH decreased to approximately an order of magnitude increase with each decrease in pH by 2pH units. The dissolution process was observed to be stoichiometric under all conditions, indicating that the mechanism by which rates are increased was not due to preferential complexation of aluminium, but rather by an increase in the overall solubility of feldspar in the neutral pH region. This regime of increased rate of reaction of feldspar coincides with that expected to be naturally buffered by the introduction of organic acids into a sandstone reservoir system.