Fenoterol and salbutamol actions on guinea-pig myometrium: effects of ovarian steroids.
Responses of isolated preparations of longitudinal myometrium from the guinea-pig to fenoterol, salbutamol and isoprenaline were examined. Virgin adult guinea-pigs were treated (i) with oestradiol cypionate 20 micrograms/kg s.c. thrice weekly for two weeks; or (ii) as in (i) plus progesterone 3 mg/animal for the last four days. Other animals (diestrous; cycle days 6-10) were untreated. The order of potency of the agonists in inhibiting field stimulation-induced contractions of the preparations (isoprenaline greater than or equal to fenoterol greater than salbutamol) indicated interaction with beta 2-adrenoceptors. Oestrogen treatment enhanced the potency of isoprenaline 5-fold. Treatment with oestrogen plus progesterone enhanced the potency of all agonists 10- to 30-fold, and increased the mean maximum response to salbutamol. The mean pKD values for displacement by fenoterol of binding of (-)-[125I]cyanopindolol to membrane preparations from animals in both treatment groups were 5.57-5.92. These results raise the possibility that progesterone may enhance the coupling of beta 2-adrenoceptors to transduction mechanisms in the longitudinal myometrium from oestrogen-primed guinea-pigs.
Department of Pharmacology, Monash University, Clayton, Victoria, Australia.
G J
GJ
Mammen
G M
GM
Handberg
M E
ME
Story
J N
JN
Pennefather
D000420:Albuterol / Q000494:pharmacology*; D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D004967:Estrogens / Q000494:pharmacology*; D005260:Female; D005280:Fenoterol / Q000494:pharmacology*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes; D020120:Iodocyanopindolol; D007545:Isoproterenol / Q000494:pharmacology; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism; D009215:Myometrium / Q000187:drug effects*; D010869:Pindolol / Q000031:analogs & derivatives
D004967:Estrogens; D007457:Iodine Radioisotopes; D005280:Fenoterol; D020120:Iodocyanopindolol; D010869:Pindolol; D007545:Isoproterenol; D000420:Albuterol