We prepared chemically skinned uterine muscle fibers from both horns of unilaterally pregnant rats and investigated the effect of gestation on the Ca²⁺ sensitivityt of the Ca²⁺-induced contraction. The Ca²⁺ sensitivity was defined as the pCa (minus logarithm of free calcium concentration) required for half maximum activation of force production. Gravid horns did not show any statistical difference in the Ca²⁺ sensitivity between normal pregnant and unilaterally pregnant rats. Non-gravid horns of unilaterally pregnant rats before Day 14 of gestation showed the same behavior in the Ca²⁺ sensitivity as horns of normal pregnant rats. After Day 15 of gestation the Ca²⁺ sensitivity of non-gravid horn also increased but significantly less than that of gravid horn.
Taking into account the hormonal situation, the present results suggest that some local factors, such as an increased size of conceptus (fetus and placenta) and/or intercellular binding conditions of myometrium modulated by the gap junction formation and the appearance of connexin molecules, may also be requisite for the regulation of the contractile activity associated with parturition and delivery of the fetus and placenta.

View full abstract

Cells of guinea pig ileal longitudinal muscle layer were dispersed by treating the minced tissue with highly purified collagenase and papain. The cells were spindle shaped, 100 to 150μm long and 5 to 10μm wide. Contractility of the dispersed cells was determined by “cell adhesion method” resulting that the cells were contracted by carbachol in a dose-dependent manner, but sensitivity and degree of the contraction were different in each cell. Binding assay method resulted that Kd values did not change by treatment with collagenase and papain. These results indicate that contractility of each cell in the tissue is originally different and dispersion of the cells does not affect on the cell contractility.

View full abstract

The effect of buprenorphine on the interdigestive myoelectric complex (IMC) was studied by gastrointestinal electromyogram in 3 mature mongrel dogs. The electromyo-grams were used to study the IMC cycle and total elapsed time (TET).
Buprenorphine had very strong hyperkinetic action on the gastointestinal tract at doses of 1 and 2μg/kg which revealed phasic contraction, but since this action disappered when atropine was administered. The phasic contraction originated in the upper jejunum just under the ligament of Treitz and then showed a migration pattern of J → D and J → I in 11 out of 23 cases (47.8%), D → J → I in nine cases (39.1%), J → D → J → I in one case and no response in two cases. TET (min) showed a mean value of 90.3± 11.2 (n=23), which was not significantly different from the controls (106.1±14.3) (n=24), but tended to be longer (0.1>p>0.05). After administration of buprenorphine at a dose of 20, μg/kg, phasic contraction migrated to ileum, which was disappered an interval of 6-7 hours until next IMC. At low doses of buprenorphine were administered after a meal, the postprandial pattern was restored and converted to fasted pattern only one IMC cycle.
Buprenorphine is partial agonist for the μ receptor. Ahmad et al.(1989) reported that α2 adrenergic receptor and opiate receptors (mainly μ) were presented in submucosal plexus. In concludes that α2 adrenergic activity and other humoral factors seems to take an important role for the initiation of phasic contraction and to control maintenance of IMC cycle.

View full abstract

Effects of prostaglandin El, E2 and F2α (PGE1, PGE2 and PGF2α) on the changes in the adenylate cyclase (AC) activities of rabbit urinary tract tissues were studied in order to clarify whehter the PGs' actions are mediated by cAMP in the urinary tract. AC activities were measured by the method of Salomon et al., The three PGs studied were all found to increase the AC activities dose-dependently in the renal pelvis, ureter, bladder dome and bladder base. Among the changes in AC activities, PGE1 and PGE2 significantly increased the AC aicivities of the renal pelvis and ureter. PGE1 significantly increased the AC aicivities of the bladder dome. It was reported that Ca²⁺ influx plays an important role in the PGs' action on the urinary tract. Our data suggest that the PGs act on the urinary tract via cAMP as well as Ca²⁺ influx

View full abstract