The adrenergic response of the myometrium and concentration of adrenergic receptors in influenced by exogenous gonadal steroids in rabbit uteri.
In human studies, it was also observed many years ago that the uterine contractile response to catecholamine stimulation could be modulated by changes in the gonadal steroid environment.
The ability to inhibit uterine contractions by activation of β-adrenergic receptor(myometrial relaxation)has clinical applications for theatment of preterm labor.
In order to prove the hypothesis that endocrine changes at different phases of the reproductive cycle and gestation might alter the β-adrenergic receptor concentration and affinity, we quantitated β-adrenergic receptor concentration and
affinity
in
myometrium from women during the mid-follicular phase, mid-luteal phase, in postmenopausal women and from women at term pregnancy.
Using the radiologand idione 125-labeled iodocyanopindolol with high specific activity and high affinity, the β-adrenergic receptor concentrations were determined.
@ES The results were as follows;
@EN 1. β-adrenergic receptor concentration and dissociation constant (Kd)were 63.4±22.2fmol/mg protein and 32.4±13.6pmol/L, respectively from women during the mid follicular phase (estradiol:75~75pg/ml, progesterone: <1ng/ml) of the cycle
which
corresponded to pure but mild estrogen stimulation.
2. β-adrenergic receptor concentration and dissociation constant (Kd) were 40.8±12.7fmol/mg protein and 30.8±11.7pmol/L, respectively form women during the midluteal phase (estradiol; 100~300pg/ml, progesterone; 5~20ng/ml)of the cycle which
correspond to increased estrogen stimulation, combined with progestestational stimulation.
3. β-adrenergic receptor concentration and dissociation constant (Kd) were 52.8±11.0fmol/mg protein and 28.1±8.1pmol/L, respectively from women in postmenopaual phase(estradiol;10~20pg/ml, progesterone;<0.1ng/ml)which are characterized by low
circulating levels of gonadal steroid hormones.
4. β-adrenergic receptor concentration and dissociation constand (Kd) were 32.5±10.3fmol/mg protein and 36.9±15.7pmol/L, respectively from women with term pregnancy(estradiol; 10~45ng/ml, progesterone, ;75~250ng/ml)which are characterized by
very
high levels of both estrogen and progesterone.
5. The concentration of β-adrenergic receptor during the mid-follicular phase were significantly increased compared with those during the mid-luteal phase and at term pregnancy.
6. The concentration of β-adrenertic receptor at term pregnancy were significantly decreased compared with those from the non-pregnancy myometrium. But there was no significant difference in dissociation constant (Kd) among the mid-follicular
phase,
midluteal phase, postmenopausal and term pregnancy.
The findings suggest that the β-adrenergic receptors in the myometrium might be modulated by endogenous gonadal steroid hormones. But the alteration of myometrial contractility during menstrual cycle and pregnancy may not be directly mediated by
β-adrenergic system.
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