Myometrial alpha 1-adrenoceptors in pregnant guinea pig: their distribution and increased number.
There is evidence for an excitatory influence in pregnant and parturient myometrium mediated by alpha 1-adrenoceptors. Despite this there are no reports of direct measurement of changes in the density of these receptors throughout pregnancy. Indirect evidence could suggest a fall early in gestation followed by a sharp rise near term. Hence, to follow pregnancy-related changes, [3H]prazosin was employed in this study to measure alpha 1-adrenoceptors in guinea pig myometrium. High-affinity [3H]prazosin binding [dissociation constant (Kd) = 0.51 +/- 0.05 nM (n = 29)] displayed the pharmacological characteristics of alpha 1-adrenoceptors and yielded linear Scatchard plots, which in nonpregnant myometrium indicated a maximum binding density (Bmax) of 48.6 +/- 6.1 fmol/mg protein (n = 5). At all times during pregnancy alpha 1-adrenoceptor density was approximately 40% higher than the nonpregnant value. This, together with uterine growth, resulted in a progressive increase in total alpha 1-adrenoceptor population of up to 34-fold with a mean value of 7.54 +/- 2.26 pmol/uterus (n = 6) at term (67 +/- 2 days). This slow rise in receptor number does not suggest a major role in the processes triggering labour in this species. The distribution of alpha 1-adrenoceptors in tubal, perifetal, and cervical regions was similar in the 60-day pregnant uterus. As much of the uterus is not innervated at this time, a considerable proportion of these receptors are probably extrasynaptic.
Arkinstall
S J
SJ
Laboratory of Cellular and Developmental Physiology, University of Oxford, Headington, United Kingdom.
Jones
C T
CT
D000818:Animals; D005576:Colforsin / Q000494:pharmacology; D005260:Female; D006168:Guinea Pigs; D007700:Kinetics; D009215:Myometrium / Q000502:physiology*; D009928:Organ Specificity; D011224:Prazosin / Q000378:metabolism; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D012016:Reference Values; D014599:Uterus / Q000378:metabolism
D011942:Receptors, Adrenergic, alpha; D005576:Colforsin; D011224:Prazosin