Pyridinolcarbamate, a bradykinin antagonist in veins. A preliminary report on pharmacologic and clinical observations

Bradykinin modulation of a spinal nociceptive reflex in the rat

Bradykinin (BK) is a potent algesic compound. Therefore, we hypothesized that BK, acting as a peripheral noxious stimulus, would attenuate or inhibit responses to another noxious stimulus. When administered intravenously (i.v.) to rats lightly anesthesized with pentobarbital, BK produced a dose-dependent (12-144 micrograms/kg) inhibition of the nociceptive tail-flick (TF) reflex. BK also produced a dose-dependent decrease in mean arterial blood pressure, a subsequent increase in heart rate and an increase in the rate of respiration. The latency to the maximal effect of BK on the TF reflex was 10 s and was occasionally preceded by pseudoaffective responses at doses greater than 48 micrograms/kg BK. Neonatal treatment with capsaicin (50 mg/kg, subcutaneous) significantly attenuated BK-produced inhibition of the TF reflex indicating that BK was acting via peripheral afferents to inhibit the TF reflex. Reversible cold block or complete spinal transection at a low thoracic level (T9-12), but not reversible cold block at a high cervical level (C1-2), significantly attenuated BK-produced inhibition of the TF reflex, suggesting that BK activates afferents which enter the spinal cord between C2 and T9. Pretreatment with intrathecally administered phentolamine (30 micrograms), an alpha-adrenoceptor antagonist, or methysergide (30 micrograms), a non-selective serotonin receptor antagonist, did not alter BK-produced inhibition of the TF reflex, further supporting the absence of activation of descending systems from the brainstem by i.v. BK. While coadministration of PGE2 and BK significantly potentiated BK-produced inhibition of the TF reflex, neither bilateral removal of the stellate ganglion nor bilateral cervical vagotomy significantly affected the inhibitory action of i.v. BK on the TF reflex. These results suggest that i.v. BK inhibits the nociceptive TF reflex by activation of capsaicin-sensitive visceral afferents entering the spinal cord between C2 and T9.

Bradykinin receptor antagonists

Bradykinin and its active metabolites are produced at the sites of their actions by kallikreins. They potently elicit a variety of biological effects: hypotension, bronchoconstriction, gut and uterine contraction, epithelial secretion in airway, gut, and exocrine glands, vascular permeability, pain, connective tissue proliferation, and eicosanoid formation. These effects are mediated by at least two broad classes of receptors. The most common is the B2 subtype. The Stewart and Vavrek peptides characterized by a DPhe7 substitution have provided powerful tools for study of bradykinin's actions by competitively and specifically blocking bradykinin B2 receptors. The significance of kinins in certain human diseases is being explored using these new tools and potential therapeutic agents. At present, human clinical trials are underway to test the usefulness of bradykinin receptor antagonists in the symptoms of the common cold and in the pain associated with severe burns. Trials for use in asthma will be initiated in 1990.

Role of plasma and serum proteases in the degradation of elastin

Accelerated proteolysis of tropoelastin and elastin occurs in the major arteries of chicks fed copper-deficient diets. Signs of elastin degradation are not obvious in normal arteries of copper-supplemented chicks. It is proposed that the sources of proteases that effect elastin degradation are from plasma and serum. Both calcium-dependent proteases and kallikrein were effective in degrading tropoelastin and partially crosslinked insoluble elastin into peptides similar to those detected in aortic extracts from copper-deficient chicks. As dietary copper deficiency progresses it is also possible to detect elastin peptides in plasma.

Pyridinolcarbamate and experimental atherosclerosis. Correlation of hypocholesterolemic and antiatherogenic effects

Rabbits were maintained for 12 weeks on either a control or hypercholesteremic dietary regime, or on comparable diets supplemented with pyridinolcarbamate (PDC) at a level of 30 mg/kg body weight/day. Blood was obtained from all rabbits prior to study and at two-week intervals for analysis of serum cholesterol, phospholipid phosphorus and triglycerides. Animals from each group were sacrificed at 4-week intervals for quantitative assessment of the degree of atherosclerotic involvement of the aorta. All animals in the four groups consumed their entire daily allowance (100 g) of their respective diets, and weight gains throughout the feeding period were comparable in the 4 groups. PDC given with the control chow diet had no effect on serum cholesterol levels but did result in persistent decrease in serum triglycerides and a variable decrease in serum phospholipids during the 12-week feeding period. None of the rabbits on the chow diet, with or without PDC, had any evidence of aortic lesions during the experimental period. Rabbits fed 1% cholesterol administered with chow exhibited markedly elevated levels of serum cholesterol and phospholipids, while serum triglycerides were not significantly different than in the control group. In these animals there was a rapid and progressive increase in aortic atherosclerosis throughout the study, and at 12 weeks plaque involvement was 74 +/- 8% of the aortic surface. Addition of PDC to the 1% cholesterol--chow diet resulted in significantly lowered levels of serum cholesterol and phospholipids, but these remained elevated compared to the control levels. There was also a dramatic reduction in the rate and extent of aortic plaque formation. Thus, after 12 weeks on diet, only 27 +/- 6% of the aortic surface showed evidence of atheroma. The data suggest that PDC significantly decreases the hypercholesteremia resulting from feeding 1% cholesterol to rabbits, and that this may be largely responsible for the antiatherogenic effect of this drug.

The effects of an anti-atherosclerotic drug, pyridinolcarbamate, on heart, vascular and brain biogenic amines

The anti-atherosclerotic drug pyridinolcarbamate was investigated in the rat for its effects on heart, blood vessel and brain biogenic amines. The drug increased the concentration of noradrenaline in all tissues and of noradrenaline and 5-hydroxytryptamine in the brain. The possibility of a link between biogenic amines and atherosclerotic disease is discussed.