Study of the Adrenergic reactivity of the anococcygeal muscle in spontaneously hypertensive rats.

The experiments in the present work, representing a part of a wider study of the reactivity of smooth muscles of spontaneously hypertensive rats, were carried out on anococcygeal muscles of Wistar male and female normotensive rats (NTR) and on spontaneously hypertensive rats (SHR), divided in two age groups: young -2.5 to 4 months, and adult -6 to 12 months. The effects of noradrenaline (NA), isoprenaline (IPNA) and phentolamine (Ph) were studied in parallel experiments on smooth-muscle preparations of NTR and SHR. NA (1 x 10(-10)-1 x 10(-4) M) and IPNA (1 x 10(-4)) caused stronger contractions in NTR preparations. The affinity of alpha-adrenoreceptors to NA was increased in the SHR preparations. Ph (1 x 10(-8)-1 x 10(-6) M) inhibited more markedly the NA-contractile effects on smooth muscles of young male SHR. The inhibitory action of Ph On IPNA-induced contractions was less manifested on SHR anococcygeal muscles. It is seen from the results obtained that the adrenergic reactivity of SHR anococcygeal muscle is reduced, which is in agreement with the data in the literature and with our earlier assumption concerning the mosaic character of the specific features of the adrenergic transmission in SHR. The established increased affinity to the transmitter of the alpha-adrenergic receptors in SHR probably represents a peculiar compensatory mechanism for facilitating the adrenergic neurotransmission with reduced capacity of the smooth-muscle effector system to transform the stimulus generated during contraction.