Solubilization, gel filtration and sedimentation behaviour of prolactin receptors from human ovarian tissue.

Receptors for 125I-labelled human prolactin have been identified in the crude membrane fraction isolated from human ovarian tissue. The non-ionic detergent Triton X-100, has been used to solubilize the membrane fraction. The presence of the receptor in the detergent extract was demonstrated by gel filtration and sucrose density gradient centrifugation. The binding was time-temperature dependent, being maximal at 23 degrees C after 15 h of incubation. Large amounts of other peptide hormones did not inhibit the binding of 125I-labelled human prolactin. The binding Scatchard analysis demonstrated that the affinity of the soluble receptor (Ka 1.13 +/- 0.15 X 10(10) M-1) for the labelled hormone was slightly greater than that of the crude membrane fraction (Ka 0.91 +/- 0.12 X 10(10) M-1). The binding capacity of the solubilized receptor was also significantly greater than that seen in the particulate before solubilization. The apparent Stokes radius of the solubilized receptor was estimated to be 57 A and that the hormone-receptor complex 60 A. The sedimentation coefficient of the solubilized receptor was 7.0 +/- 0.1 s, whereas that of the hormone-receptor complex was 7.5 +/- 0.2 s.

Protective role of heparin on in vitro functional aortic response in Watanabe heritable hyperlipidemic rabbits.

The effects of prolonged in vivo heparin treatment upon vasomotor responses and content of cholesterol and energy related compounds were studied in isolated thoracic and abdominal aortas from Watanabe heritable hyperlipidemic (WHHL) rabbits. Unfractionated heparin was administered subcutaneously (2 mg/kg twice a day) to 3-month-old WHHL rabbits for a period of 6 months. A group of WHHL rabbits was treated with saline solution and considered as control. Aortic cholesterol infiltration and serum cholesterol were not significantly decreased by the prolonged heparin treatment. In heparin-treated WHHL rabbits, the in vitro aortic endothelium-dependent relaxation produced by acetylcholine or calcimycin (A 23187) was greater than in saline-treated WHHL group. ATP-induced aorta relaxation (endothelium-dependent and endothelium-independent) did not vary significantly in the two groups of WHHL rabbits, even after mechanical removal of endothelium. Also the noradrenaline-induced aorta contraction did not vary between the two groups of WHHL rabbits. No significant variation in energy-related compounds (except for ADP) was found in the aortic arch. These results suggest that heparin produces a protective effect on aortic tissue by acting mainly at endothelial level.

Aortic response to relaxing agents in Watanabe heritable hyperlipidemic (WHHL) rabbits of different age.

Serum and aortic tissue cholesterol levels in parallel with aortic relaxation to endothelium-dependent and independent drugs were determined in Watanabe heritable hyperlipidemic (WHHL) rabbits in comparison with New Zealand (N.Z.) normocholesterolemic rabbits, aged 4-14 months. Serum cholesterol was elevated (626 +/- 99 mg/100 ml) in 4-6-month-old WHHL rabbits and significantly lower in 12-14-month-old animals (344 +/- 51 mg/100 ml). Cholesterol infiltration in thoracic aorta was high in young WHHL compared with N.Z. rabbits (0.88 +/- 0.3 mg/100 mg fresh tissue vs. 0.08 +/- 0.003 mg/100 mg, respectively) and it did not vary with age. In N.Z. rabbits, serum and aortic cholesterol levels were low from 4 to 14 months of age. The aortic relaxation to acetylcholine (0.03-3 microM) on EC50 noradrenaline precontracted rings was similar in 4-6-month-old WHHL and N.Z. rabbits of the same age. In WHHL rabbits, the relaxation to acetylcholine was significantly reduced in 7-11- (-35% at maximum) and in 12-14-month-old rabbits (-40% at maximum). In N.Z. rabbits the response to acetylcholine was not modified in the 3 age groups. The relaxation to ATP (30 microM to 3 mM) was reduced by age both in N.Z. and in WHHL rabbits, but in 12-14-month-old WHHL rabbits the maximal relaxing response was significantly more elevated than in age-matched N.Z. rabbits (50.1 +/- 2.5% vs. 35.1 +/- 3.2%, respectively). The aortic relaxation to NaNO2 (10 microM to 3 mM) was reduced by age both in N.Z. and in WHHL rabbits.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelium-dependent relaxation, cholesterol content and high energy metabolite balance in Watanabe hyperlipemic rabbit aorta.

Functional and metabolic parameters of thoracic aorta from Watanabe heritable hyperlipemic (WHHL) rabbits (aged 11-14 months) were investigated in vitro. The aortic preparations, normally responsive to noradrenaline, showed a diminished response to the endothelium-dependent agent, acetylcholine, in comparison with control preparations from age-matched New Zealand rabbits (maximal relaxation: 33 +/- 4% in WHHL vs. 52 +/- 2% in controls: P less than 0.005). ATP relaxant effect (only partially endothelium-dependent) was unimpaired in WHHL aorta, and it was much higher than in controls (maximal response: 63 +/- 6% vs. 37 +/- 3%, respectively; P less than 0.005). The response to NaNO2, an endothelium-independent relaxant, was unchanged in WHHL aortas. Acetylcholine-induced response was found to be inversely related to the degree of total cholesterol infiltration in aorta (r = -0.62, P less than 0.05). No correlation was observed between either total serum cholesterol or triglycerides and ACh-induced response. Furthermore, the concentration of adenine nucleotides and nucleosides in the aortic tissue of WHHL rabbits was lower than in controls, indicating a loss of energy balance. The results indicate a functional damage induced by genetic hyperlipidemia on endothelium-dependent relaxation and an impairment of energy-rich phosphate metabolism of the aortic wall. The relationship between functional and metabolic parameters is not yet clarified.

Effect of selective agonists and antagonists on atrial adenosine receptors and their interaction with Bay K 8644 and [3H]-nitrendipine.

1. (-)-N6-phenylisopropyladenosine (R-PIA) and N6-cyclohexyladenosine (CHA), highly selective agonists at A1-adenosine receptors, 5'-N-ethyl-carboxamidoadenosine (NECA), a non-selective agonist at A1 and A2 receptors, and 2-phenylaminoadenosine (CV-1808), a selective A2 agonist, were compared in spontaneously beating and electrically driven atria. R-PIA, CHA and NECA inhibited contraction in both preparations. CV-1808 was not effective up to 500 nM. 2. 1,3-Dipropyl-8-cyclopentylxanthine (DPCPX), a new selective A1 receptor antagonist, competitively inhibited the effects of the adenosine agonists, at low concentrations (IC50 less than 1 nM). 3. CHA and NECA were able to inhibit the positive inotropic effect of Bay K 8644 both in spontaneously beating and in electrically driven atria. 4. R-PIA, CHA and NECA (agonists), 8-phenyltheophylline (PT) and DPCPX (antagonists), failed to influence [3H]-nitrendipine binding on microsomal membranes from guinea-pig atria and ventricles in a range of concentrations from 1 nM to 100 microM. 5. The data support the existence of A1 receptors in atrial tissue. No evidence for a direct interaction between adenosine analogues and Bay K 8644 was found at the level of slow calcium channels. Adenosine analogues appear to antagonize the effects of Bay K 8644 indirectly by activation of A1 receptors.

Potassium channel blockers differentially affect carbachol and (-)-N6-phenylisopropyladenosine on guinea-pig atria.

1. The effect of three different potassium channel blockers (tetraethylammonium, TEA; 4-aminopyridine, 4-AP; and apamin) and of variations in the concentration of K+ and Ca2+ in the medium, have been studied on the responses of guinea-pig isolated atria to (-)-N6-phenylisopropyladenosine (R-PIA), a stable adenosine A1-receptor agonist, and to carbachol, a muscarinic agonist. R-PIA and carbachol showed the same negative inotropic effects over a similar range of concentrations (3-300 microM), both in spontaneously beating and in electrically driven atria. 2. TEA (0.1 to 20 mM) and 4-AP (0.3 to 3 mM), both antagonized the negative inotropic and chronotropic effects of carbachol in a concentration-dependent manner. In contrast, these compounds failed to inhibit the effects induced by R-PIA. Apamin, a specific blocker of a low conductance Ca2+-activated K+ channel, was ineffective in accordance with the absence of these channels in atrial tissue. 3. TEA (0.1 to 20mM) inhibited the negative inotropic effect of carbachol, but not that of R-PIA, in atria paced and depolarized by a high K+ medium (22 mM). In this preparation Na+ current is abolished and the contraction induced by noradrenaline and electrical stimulation is solely dependent on Ca2+ influx currents. 4. Stepwise addition of Ca2+ to a calcium-depleted perfusing medium of electrically driven atria, induced a positive inotropic effect which was inhibited by R-PIA. In contrast, carbachol had no effect. 5. In agreement with our previous study, the data suggest that R-PIA acts on isolated atria by inhibiting Ca2+ influx through L-channels.

Dual effect of ATP and UTP on rat atria: which types of receptors are involved?

The effects of adenine compounds and UTP were examined in electrically driven rat left atria. ATP, ADP, AMP, adenosine and UTP caused a dual inotropic effect: first a rapid decrease in contractility, and second an increase in contractile tension. alpha,beta-Methylene ATP caused an increase in contractile tension only, whereas 2-methylthio-ATP only induced a negative inotropic effect, 1,3-Dipropyl-8-cyclopentylxanthine inhibited the negative effects of ATP and adenosine, whereas 3,7-dimethyl-1-propargylxanthine did not influence the effects of ATP. Suramin but not reactive blue 2 antagonized the positive inotropism induced by ATP and alpha,beta-methylene ATP. Suramin also abolished the positive inotropic effect induced by UTP. These results demonstrate that ATP may induce negative inotropism directly by an action on A1-adenosine receptors and positive inotropism by an action on P2x-purinoceptors. UTP induces a positive inotropic effect mediated by suramin-sensitive receptors.

Phentolamine and hypoxia: modulation of contractility and alpha 1-adrenoceptors in isolated rat atria.

The hypoxia-induced effects on the binding sites and affinity constant of adrenoceptors, in the presence and absence of phentolamine, were determined for atrial membranes of hearts from normal and genetically hyperlipidaemic Yoshida (YOS) rats. Atrial function was also measured during normoxia and hypoxia, in the presence and absence of phentolamine. Hypoxia increased alpha 1-adrenoceptor density in atrial membranes of normal rats (Bmax 10.6 to 26.7 fmoles/mg protein). Phentolamine prevented the increase in the Bmax of alpha 1-adrenoceptors and increased the equilibrium dissociation constant of these receptors (KD 0.17 to 0.53 nmol/l). Beta-adrenoceptors did not change during hypoxia, but the Bmax was slightly increased (26%) in the presence of phentolamine. Thus, the alpha 1/beta ratio increased from 0.40 in normoxia to 1.06 in hypoxia. In normoxic atria from YOS rats, the alpha 1/beta ratio was already elevated (0.86) in comparison to control rats (mainly due to a higher density of alpha 1-adrenoceptors in atrial membranes from YOS rats). This ratio was not modified by hypoxia (0.84), but decreased when phentolamine was present (0.30). Hypoxia reduced the force of contraction and increased diastolic tension of atria of normal rats, while the sinus rate was not significantly modified. Phentolamine abolished the increase in diastolic tension and reduced the negative effect of hypoxia on contractile force. In YOS rat atria, functional parameters were modified by hypoxia in a qualitatively similar way to that of normal rat atria.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of vitamin A compounds in bovine eyes after bleaching adaptation.

A seasonal increase in the amount of bleached rhodopsin caused, in living animals, by the seasonal increase of the intensity of sunlight in the early morning before the calves are killed, was verified in the bovine eyes subjected to the present study. This was used as a means of assaying distribution and isomer composition of esterified and unesterified retinol in eyes from animals light-adapted to a different extent under environmental conditions. The progressive increase of bleached rhodopsin results in a parallel increase of all-trans-retinol in retina and of both all-trans- and 11-cis-retinyl esters in pigment epithelium. Analytical subcellular fractionation of RPE homogenate reveals that retinyl esters accumulate without an exclusive subcellular localization in nuclear, mitochondrial/lysosomal and microsomal fractions. Whatever the amount of bleached rhodopsin, only small and constant amounts of retinyl esters are found in the soluble fraction of RPE, entirely under the all-trans configuration. When a considerable portion of rhodopsin is bleached (about 70%), substantial amounts of all-trans-retinol, along with minor amounts of 11-cis-retinol, accumulate in RPE subcellular organelles. The in vitro bleaching of bovine eyes results in a distribution of retinoids between retina and RPE which appears different from that detected in eyes naturally bleached to the same extent.

Prolonged inhibition of nitric oxide synthesis in Yoshida hyperlipidemic rat: aorta functional and structural properties.

To test whether inhibition of nitric oxide synthesis, associated with high levels of plasmatic lipids, can induce atherosclerotic lesions and phenotypic changes in smooth muscle cell composition in the aortic wall of an atherosclerotic-resistant species such as the rat, an inbred strain of hyperlipidemic Pittsburgh Yoshida rat was subjected to prolonged treatment (2 months) with the nitric oxide-synthase inhibitor L omega-nitro-arginine-methyl ester or with L-arginine. The two types of in vivo treatments were not able to modify in vitro aortic endothelium-mediated relaxation induced by acetylcholine or calcium-ionophore A-23187, the endothelium-independent sodium nitrite relaxation and the contractile response to serotonin. Histology and lipid infiltration of vascular specimens showed that L omega-nitro-arginine-methyl ester in vivo treatment did not induce any significant change in the aortic wall. Monoclonal antibodies to myosin isoforms and immunofluorescence procedures revealed the presence of an immature smooth muscle cell subpopulation in aortic specimens from saline-treated Pittsburgh Yoshida rats, whose expansion has been related in other species to atherogenesis. This peculiar cell phenotype disappeared in our animal model after prolonged L omega-nitro-arginine-methyl ester treatment. These data indicate that, despite interference with endothelium-mediated nitric oxide synthesis, atherosclerosis does not develop in this animal model and furnish for the first time a biological justification for atherogenesis resistance of rat, i.e., the lack of activation of an immature aortic smooth muscle cell population which in atherosclerosis-prone species is involved in lesion formation.

Electrophysiological instability in the acute phase: prognostic significance of early ventricular fibrillation in acute myocardial infarction.

BACKGROUND: In the prognostic stratification of patients affected by AMI is important to evaluate, besides the assessment of left ventricular function and residual ischemia, the presence of electrophysiological instability. METHODS: We have analysed 15 patients all affected by AMI complicated by early ventricular fibrillation. During the hospital phase we evaluated the E.F.% (ECHO) and the presence of late ventricular potentials (SAECG). After hospital discharge we followed up the patients for 6 months. RESULTS: None of the patients died during the hospital phase while the posthospital cardiac mortality was 20%. The three patients dead during the follow-up had an AMI localized in the anterolateral wall of the left ventricle, an E.F.% less than 40% and LVP positive in the hospital phase. Besides the clinical course was complicated by cardiac failure. CONCLUSIONS: We conclude that these three patients are a "high risk profile subgroup" and should be submitted to extensive evaluation with cardiac catheterization, coronary arteriography and programmed ventricular stimulation.

Purine- and nucleotide-mediated relaxation of rabbit thoracic aorta: common and different sites of action.

The mechanisms of the relaxant effect of purines and pyrimidines in New Zealand rabbit isolated aorta were investigated at endothelial and smooth muscle cell levels. Endothelium-mediated relaxation by ATP was only partially inhibited by the P2-purinoceptor antagonist suramin (0.1 mM). The pyrimidine UTP produced vasodilation by acting at the endothelial level and relaxation was not antagonized by suramin (0.1 mM). This effect was not mediated by P2 purinoceptors, indicating that UTP, like ATP to a certain extent, produces relaxation via an endothelium nucleotide (N) pyrimidinoceptor. ATP, ADP, AMP, adenosine, 5'-N-ethylcarboxamidoadenosine (NECA) and inosine were all active as relaxants on smooth muscle. The NECA relaxant effect was not antagonized by P1-purinoceptor antagonists 3,7-dimethyl-1-propargylxanthine (50 microM) or 1,3-dipropyl-8-(2-amino-4-chlorophenyl)xanthine (5 microM), excluding a P1-mediated effect. P2-related activity was excluded because adenosine-mediated relaxation was not antagonized by suramin (0.1 mM). UTP was ineffective as a relaxant at smooth muscle level, thus excluding the presence of muscular nucleotide (N) pyrimidinoceptor and suggesting a P3 purinoceptor. The rank order of potency of this muscle purinoceptor was NECA > adenosine > ATP approximately equal to ADP approximately equal to AMP approximately equal to inosine.

Effects of bendazac L-lysine salt on some metabolic enzymes of glutathione in the rabbit lens after X-irradiation.

The effect of (1-benzoyl-1H-indazol-3-yl)oxylacetate L-Lysine (bendazac-lysine) on some enzymatic activities involved in the metabolism of reduced glutathione (GSH) was studied in the rabbit lens during developing cataract induced by a single dose of X-rays (2000 rads). The specific activities of glutathione reductase (G.R.), glutathione peroxidase (GSH.Px) and glutathione S-transferase (GSHS-tr.) do not change following irradiation and treatment with bendazac-lysine. The activity of the same enzymes expressed as a function of water soluble proteins (WSP) per lens significantly decreases (P less than 0.01) as compared to controls in the irradiated lens not treated with bendazac-lysine (ILNTB) at the 8th week, whereas no significant decrease as compared to controls is observed in the irradiated lens treated with bendazac-lysine (ILTB). In the ILNTB the specific activity of glucose-6-phosphate dehydrogenase (G6PDH) is reduced by 10% after 0.3 weeks and by 29% after 12 weeks. In the ILTB the specific activity of G6PDH is reduced by 8% after 0.3 weeks and by 14.5% after 12 weeks. The specific activity of superoxide dismutase (SOD) in the ILNTB is reduced by 19% after 0.3 weeks and reached 31% after 12 weeks. In the ILTB the specific activity of SOD is reduced by 11% after 0.3 weeks and 19.8% after 12 weeks. The mechanism of protective effect of bendazac-lysine on cataract is discussed.

Synthesis, characterization, crystal structure and preliminary reactivity behaviour of new heteropolytopic ligands based on the 1,3,5-triazine spacer and pyrazolyl, tris-pyrazolylmethyl and tris-pyrazolylethoxy bonding fragments.

Four new potentially polytopic nitrogen donor ligands based on the 1,3,5-triazine fragment, L(1)-L(4) (L(1) = 2-chloro-4,6-di(1H-pyrazol-1-yl)-1,3,5-triazine, L(2) = N,N'-bis(4,6-di(1H-pyrazol-1-yl)-1,3,5-triazin-2-yl)ethane-1,2-diamine, L(3) = 2,4,6-tris(tri(1H-pyrazol-1-yl)methyl)-1,3,5-triazine, and L(4) = 2,4,6-tris(2,2,2-tri(1H-pyrazol-1-yl)ethoxy)-1,3,5-triazine) have been synthesized and characterized. The X-ray crystal structure of L(3) confirms that its molecular nature consists of a 1,3,5-triazine ring bearing three tripodal tris(pyrazolyl) arms. L(1), L(2), and L(4) react with Cu(I), Cu(II), Pd(II) and Ag(I) salts yielding mono-, di-, and oligonuclear derivatives: [Cu(L(1))(Cy(3)P)]ClO(4), [{Ag(2)(L(2))}(CF(3)SO(3))(2)]·H(2)O, [Cu(2)(L(2))(NO(3))(2)](NO(3))(2)·H(2)O, [Cu(2)(L(2))(CH(3)COO)(2)](CH(3)COO)(2)·3H(2)O, [Pd(2)(L(2))(Cl)(4)]·2H(2)O, [Ru(L(2))(Cl)(OH)]·CH(3)OH, [Ag(3)(L(4))(2)](CF(3)SO(3))(3) and [Ag(3)(L(4))(2)](BF(4))(3). The interaction of L(3) with Ag(I), Cu(II), Zn(II) and Ru(II) complexes unexpectedly produced the hydrolysis of the ligand with formation, in all cases, of tris(pyrazolyl)methane (TPM) derivatives. In detail, the already known [Ag(TPM)(2)](CF(3)SO(3)) and [Cu(TPM)(2)](NO(3))(2), as well as the new [Zn(TPM)(2)](CF(3)SO(3))(2) and [Ru(TMP)(p-cymene)]Cl(OH)·2H(2)O complexes have been isolated. Single-crystal XRD determinations on the latter derivatives confirm their formulation, evidencing, for the Ru(II) complex, an interesting supramolecular arrangement of the anions and crystallization water molecules.

Synthetic fragments and analogues of elastin. I. The synthesis.

The synthesis of some repetitive sequences of elastin and their simplified analogues, all comprising the structural unit Gly-X-Gly (X = Val, Leu, Ala), is described. In particular, the following peptides and polypeptides were synthesized and characterized: Boc-Gly-Val-Gly-Gly-Leu-OMe, Boc-Gly-Leu-Gly-Gly-Val-OMe, Boc-(Gly-Val-Gly-Gly-Leu)2-OMe, Boc-(Gly-Val-Gly-Gly-Leu)3-OMe, Boc-Gly-Val-Gly-Gly-OEt, Boc-Leu-Gly-Gly-Leu-OMe, Boc-Val-Gly-Gly-Val-OMe, poly(Ala-Gly-Gly), poly(Val-Gly-Gly), and poly(Leu-Gly-Gly). In every case, the synthesis was accomplished by classical procedures in solution, by using the p-nitrophenyl ester method for the polycondensation step, and the mixed anhydride or the azide methods for the coupling steps.

Synthetic fragments and analogues of elastin. II. Conformational studies.

Conformational studies on synthetic repetitive sequences and analogues of elastin are described. CD and nmr measurements gave evidence of flexible beta-turns as the dominant structural feature whose stability was found to decrease by increasing the number of repetitive units. The sequences comprised the structural unit Gly-X-Gly (X = Val, Leu, Ala), with X-Gly or Gly-Gly located at the corners of the bend. Based on that, it is proposed that these regions of elastin, unlike the proline-containing sequences, contribute to the elasticity of the protein through a classical mechanism in terms of the rotational isomeric state theory.

Effects of bendazac L-lysine salt on X-ray-induced cataract in the rabbit lens.

The effects of bendazac-L-lysine salt (bendazac-lysine) on some biochemical parameters (soluble and insoluble proteins, reduced glutathione, sulphydryl and disulphide groups, water content) in rabbit lens at different times after X-rays (2000 rads) were studied. The mature cataract (swelling and total lens opacity) developed 11-12 weeks after irradiation. In the mature cataract, the irradiated lenses not treated with bendazac-lysine (ILNTB) show a 32% increase in water content compared with controls; this increase is 12% in irradiated lens treated with bendazac-lysine (ILTB). Twelve weeks after irradiation the concentration of insoluble proteins in the controls, ILNTB and ILTB is 7.6%, 52.3% and 18.3% respectively. After 6, 8 and 12 weeks the concentration of reduced glutathione in ILNTB decreases by 23%, 81% and 92% as compared with the controls. In the ILTB the decrease is present only 8 and 12 weeks after X-irradiation and is of 55% and 69%, respectively. The sulphydryl-group content in the soluble proteins in ILNTB compared with the controls decreases by 26%, 38% and 47% after 6, 8 and 12 weeks, while in the ILTB a decrease is observed only after 8 and 12 weeks and is 6% and 12%, respectively. The decrease of the sulphydryl groups parallels the increase of the disulphide groups. This increase is already significant (P less than 0.01) after 6 weeks in the ILNTB, whereas it becomes significant in the ILTB only after 8 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)

L-Arginine does not improve endothelium-dependent relaxation inin vitro Watanabe rabbit thoracic aorta.

The findings that even a singlein vitro addition of L-arginine is able to normalize endothelium function in cerebral vessel from diet-induced hypercholesterolemic rabbits prompted us to investigate if similar results could be obtained on Watanabe rabbits thoracic aorta, in which we previously demonstrated low content of the amino acid.L-Arginine (1 mM) preincubated for 45 minutes before the addition of drugs for studing endothelium-dependent vascular relaxation, did not modify the effect of acetylcholine on aortic isolated preparations. The lack of any effect by L-arginine indicates that the amino acid deficiency is not main cause of the impairment of endothelium function. The muscarinic receptor functionality affected by atherosclerotic process and/or the increased synthesis of EDCFs could account for the reduced endothelium-dependent relaxation.

Protection of atrial function in hypoxia by high potassium concentration.

1. The effects of high extracellular potassium on hypoxia-induced atrial activity and metabolic charge were studied in isolated rat atria. 2. After hypoxia (30 min), contractile tension strongly decreased and diastolic tension increased, while frequency did not change. Adenine nucleotides and creatine phosphate levels did not change, although a significant increase in lactic acid content was observed. 3. High [K+] mostly countered the hypoxia-induced increase in diastolic tension. Moreover, in the presence of high [K+], the hypoxia-induced increase in lactic acid was not significantly different from normoxic controls. 4. Glibenclamide (0.1 microM), a selective K+ATP channel blocker, did not improve the hypoxia-induced depression of atrial function. 5. The physiopathological role of extracellular potassium during cardiac hypoxia is discussed.

Effect of calcium antagonists on isolated aorta from hypercholesterolemic Yoshida rats of different ages.

1. The in vitro thoracic aorta, precontracted with norepinephrine, KCl or PGF2 alpha of hypercholesterolemic Pittsburg-Yoshida (YOS) and normolipidemic Brown-Norway (BN) rats of two age groups (2 and 18 months), was relaxed by the calcium antagonists verapamil and nifedipine without any difference between age-matched YOS and BN rats. 2. The relaxant activity of verapamil was impaired in aged rats of both strains and with the different contractile agents. Conversely, no variation with aging of the nifedipine relaxing effect was observed on KCl-induced contraction was the nifedipine relaxant effect differently affected by age, both in YOS and BN rats. 3. In conclusion, prolonged exposure to hypercholesterolemia in YOS rat does not affect aortic response to nifedipine and verapamil. Only the aging process was able to affect vascular relaxation to calcium antagonists.