title: Cardiac beta-adrenoceptors during normal growth of male and female rats.
abstract: 1 A binding assay involving (-)-[3H]dihydroalprenolol (DHA) and KCl-washed cardiac membranes were used to assess the numbers and affinities of beta-adrenoceptors in hearts from male and female rats varying in age from about 2 weeks to 18 months. 2 Although female rats grow more slowly and attain lower adult weights than male rats, heart weights increased in approximate proportion to body weight with little sex difference. 3 As heart weight increased about three fold, beta-receptors increased three fold. Since the number of myocardial cells is believed to be nearly constant during postnatal growth, the numbers of receptors/cell presumably increases similarly. 4 As heart weight increased, the number of beta-receptors per g of tissue decreased according to the equation: total pmol/g = 4.33 - 1.43 x heart weight, equally in males and females. 5 Dissociation constants for DHA (2 to 4 nM) remained the same, and equal, in male and female rats during their growth. 6 An excellent correlation was found between the decline in beta-receptors/g tissue during growth and the decline in the area of the external sarcolemma/g tissue. The data suggest that the number of receptors per unit area remains constant during growth, and thus that cell surface area is a major factor determining normal numbers of receptors per cardiocyte.
mesh_terms: D000818:Animals; D001835:Body Weight; D004082:Dihydroalprenolol / Q000378:metabolism; D005260:Female; D006321:Heart / Q000254:growth & development*; D007700:Kinetics; D008297:Male; D009124:Muscle Proteins / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D009929:Organ Size; D011485:Protein Binding; D051381:Rats; D011941:Receptors, Adrenergic / Q000378:metabolism*; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*
chemical_list: D009124:Muscle Proteins; D011941:Receptors, Adrenergic; D011943:Receptors, Adrenergic, beta; D004082:Dihydroalprenolol