Characteristic changes of plasma proteins in the Dahl hypertensive rat strain (DS) during the development of hypertension

Evidence for a 12 kDa "Carrier Protein" for Natriuretic Hormone

The search for the elusive Na-K-ATPase-inhibiting natriuretic hormone continues. In this review, evidence is presented that isolating the carrier protein for natriuretic hormone from hypertensive plasma is a necessary first step before splitting off the final hormone. The carrier protein has a molecular weight of 12 kDa while the final hormone has a molecular weight of 408 Da. Both compounds inhibit Na-K-ATPase but the compound containing the carrier protein predominates. The question has been raised as to whether the carrier protein is in actuality proANF, a 17 kDa protein that can be split between a 14 kDa protein (the presumptive proANF) and the 3 kDa ANF.

Postsynaptic alpha 1- and alpha 2-adrenergic receptors in adrenergic control of capacitance vessel tone in vivo

The involvement of postsynaptic alpha 2-adrenergic receptors in the adrenergic constriction of the capacitance vessels was studied in anesthetized, spontaneously breathing dogs under ganglionic blockade (hexamethonium, 10 mg/kg + 10 mg/kg/hr; methylatropine, 0.5 mg/kg). Effective vascular compliance was measured as an indicator of venous tone (blood volume was varied by +/- 4 ml/kg in an 11-minute cycle of infusion, withdrawal, withdrawal, and reinfusion) and was calculated from the correlation between the observed changes in central venous pressure and the changes in blood volume. Sympathetic activity and central venous pressure were lower and effective vascular compliance was higher than values in untreated conscious dogs. The alpha 2-agonist UK 14,304 (5-bromo-6-[imidazolin-2-ylamino]-quinoxaline; 0.04 and 0.12 micrograms/kg/min; n = 6) dose-dependently lowered compliance and increased central venous pressure to levels found in conscious dogs, as did the alpha 1-agonist methoxamine (10 and 30 micrograms/kg; n = 6). Rauwolscine (alpha 2-antagonist), 0.3 mg/kg, significantly attenuated the effects of UK 14,304, but not those of methoxamine, while prazosin (alpha 1-antagonist), 0.12 mg/kg, attenuated the effects of methoxamine, but not those of UK 14,304 (n = 6 each). Under beta-blockade (nadolol, 2 mg/kg; n = 12) venous tone was increased to about physiological levels by norepinephrine, 0.15 micrograms/kg/min i.v., or by neuronal norepinephrine release induced by tyramine, 10 micrograms/kg/min i.v. These increases were significantly attenuated by prazosin as well as by rauwolscine and were abolished by a combination of both. These results indicate that postsynaptic alpha 2-adrenergic receptors (in addition to alpha 1-adrenergic receptors) are functional in the venous system in vivo and contribute substantially to adrenergic sympathetic and humoral regulation of venous tone.

Platelet thromboxane inhibition by plasma polypeptides in prehypertensive Dahl rats

Plasma from Dahl rats susceptible to salt-induced hypertension (Dahl S rats) contains inhibitory factors that reduce the release of thromboxane A2 from thrombin-activated platelets. Platelet-rich plasma from Dahl S rats on either low salt (0.11 or 0.3% NaCl) or high salt (4% NaCl) diets released about 50% less thromboxane A2 than comparable plasma from Dahl rats that are resistant to hypertension (Dahl R rats). This inhibitory activity was present even in the blood of 4-week-old completely normotensive Dahl S rats on a diet containing 0.11% low NaCl. The inhibitory activity could be transmitted to platelets of normal Sprague-Dawley rats by incubating these platelets in boiled and dialyzed plasma from Dahl S rats. Moreover, the inhibitory activity could be completely washed off the Dahl S platelets by incubation in Dahl R plasma. Thus, Dahl S plasma contains inhibitory factors that reduce platelet thromboxane A2 release. The factors are found in low concentrations even in Dahl R plasma; and in Dahl S or Dahl R plasma the factors are increased 25 to 32% by a 4% high NaCl diet. Digestion of Dahl S and Dahl R plasma with either trypsin or chymotrypsin destroyed the inhibitory factors, which have a molecular weight between 2,000 and 3,500. Twenty-four hours after bilateral nephrectomy, dialyzed plasma from both Dahl S and Dahl R rats was completely devoid of thromboxane A2 inhibitory activity. Thus, the factors appear to be heat-stable polypeptides either produced in the kidney or greatly influenced by the presence of renal tissue.(ABSTRACT TRUNCATED AT 250 WORDS)