The American journal of physiology
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We investigated in conscious, chronically instrumented dogs whether actions mediated by V1 receptors affect cardiovascular effects elicited by V2-like receptors in response to vasopressin or vasopressin analogues. Infused arginine vasopressin (AVP) (220 pg.kg-1.min-1) did not have any significant effect on arterial pressure, cardiac output (CO), and heart rate (HR) when it was preceded by administration of a V1 receptor antagonist. However, when the same antagonist was administered 1 h after the start of the same infusion of AVP, CO, and HR increased significantly above control pre-AVP values, and total peripheral resistance (TPR) fell significantly below control. ⋯ In another set of experiments, the administration of a selective V1 agonist blunted significantly the CO and HR increase as well as the decrease in TPR normally associated with injection of a selective V2 agonist. However, administration of phenylephrine did not reduce these V2-mediated effects. We conclude that there are significant interactions between V1 and V2-like receptors in the cardiovascular system of conscious dogs, whereby V1 effects appear to 1) immediately antagonize the action of V2 agonists and 2) sensitize the organism to cardiovascular effects mediated by V2-like receptors after a prolonged exposure.(ABSTRACT TRUNCATED AT 250 WORDS)
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At 37 degrees C, pH 7.4, carbonic anhydrase activity (kenz) of disrupted rat renal proximal tubules and cortical mitochondria was 2.5 +/- 0.8 (n = 3) and 0.15 +/- 0.40 (n = 3) ml.mg-1.s-1, respectively. Turnover number for renal mitochondrial carbonic anhydrase (CA V) was 24,000 s-1. CA V activity of intact mitochondria was completely inhibited by 0.15 microM ethoxzolamide (EZ). ⋯ At no pyruvate concentration was there a change in the rate of glucose production when tubules were incubated in 50 mM HCO3- buffer with 1.6 microM EZ. These data also support the hypothesis that CA V provides the HCO3- substrate for pyruvate carboxylation when there is a high rate of intracellular CO2 production and external CO2 is low. It is further concluded that the cytosolic carbonic anhydrase (CA II) and the membrane-bound carbonic anhydrase (CA IV) are not involved in glucose synthesis from pyruvate.
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Body temperature, plasma responses, and subjective ratings of thirst and hotness were studied in 5 older men (OM, 61-67 yr) and 6 younger men (YM, 21-29 yr) during 180-min thermal dehydration and subsequent 60-min rehydration (45 degrees C, 25% relative humidity). Rectal temperature (Tre) increased more rapidly and to a greater magnitude in OM, while average total body sweat rates and chest sweat rates were not significantly different. During dehydration, both OM and YM lost similar body weight (1.52 +/- 0.11 vs. 1.55 +/- 0.22%, mean +/- SE). ⋯ Within 30 min of drinking, YM had restored Pv and Posm, whereas OM showed slower responses, restoring Posm after 60 min and Pv only after a subsequent 30 min at 25 degrees C. Despite a higher Tre and greater change in Pv and Posm, OM rated themselves less thirsty and not significantly hotter than YM. These findings suggest that aging results in decreased ability to maintain Tre during heat stress and that the mechanisms comprise a combination of alterations in body fluid distribution and perception.
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The effect of verapamil (VER) resuscitation from shock on cardiac function, regional blood flow, as well as skeletal muscle transmembrane potential (TMP) and electrolyte redistribution were studied. Two hours of hypotensive shock in the dog significantly impaired cardiac function and coronary perfusion; TMP fell from 89.9 +/- 0.9 to 75.1 +/- 1.2 mV. Skeletal muscle (SMS) extracellular water decreased 40 +/- 2%, whereas intracellular sodium and chloride increased and intracellular potassium fell. ⋯ SMS calcium was lower in VER dogs (148 +/- 4 micrograms/g) compared with dogs treated with fluid alone (322 +/- 24 micrograms/g, P = 0.01). Myocardial calcium fell in all dogs after volume replacement regardless of calcium-channel blockade (VER: 148 +/- 8, Ringer: 165 +/- 17 micrograms/g; P greater than 0.05). Our data indicate a potential role for calcium-entry blockade in the treatment of hemorrhagic shock.
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Comparative Study
Arteriovenous oximeter for O2 content difference, O2 saturations, and hemoglobin content.
We combined two spectrophotometric oximeters to measure continuously and simultaneously arteriovenous O2 content difference (AVOD) as well as arterial and venous oxyhemoglobin saturations (SaO2, SvO2) and total hemoglobin concentration (Hb). AVOD of the flowing arterial and venous whole blood was determined by the method of Guyton et al. (J. Appl. ⋯ AVOD, SaO2, SvO2, and Hb were compared with the data of the arterial and venous blood sampled near the oximeter cuvettes and measured with an IL282 CO oximeter. In one dog experiment and one in vitro blood experiment, AVOD data of the same arterial and venous blood were compared by connecting the present oximeter in series with an A-VOX Systems oximeter developed by Shepherd and Burgar. The results showed that the new arteriovenous oximeter can continuously measure AVOD, SaO2, SvO2, and Hb over wide ranges with reasonable accuracy.