Role of Ca2+ on uterine force stimulated by a glycoside from the root of Dalbergia saxatilis.

Uterine muscle contraction is dependent on external Ca2+ and Ca2+ release from cytoplasmic storage sites. In this study, the mechanism of Ca2+ mobilization in uterine muscle cells by glycoside, dalsaxini, isolated from the root of D. Saxatilis was investigated in the rat. Uterine muscle contractility stimulated by dalsaxin was concentration dependent (ED50 0.13 mg/ml) and was significantly attenuated (85%; P < 0.01) in Ca(2+)-free physiological solution and in solutions containing verapamil (0.06-0.48 mumol). The small transient contraction observed in Ca(2+)-free medium was further suppressed by caffeine (2 mmol) and completely abolished in solutions containing Lanthanum chloride [(La3+), 2 mmol]. Contractions stimulated by the glycoside were unaffected by amiloride (50-83 mumol) in Ca(2+)-free and Ca(2+)-containing media. Dalsaxin also altered the pattern of uterine contraction stimulated by high potassium depolarization from fast-phasic to a sustained but transient plateau. It is concluded that dalsaxin causes uterine muscle contraction by mobilizing external Ca2+ through predominantly a voltage-dependent Ca2+ channel.

Adrenergic influence of uterine muscle contractions stimulated by a glycoside from the root of Dalbergia saxatilis.

The mechanism of uterine muscle contraction stimulated by a triterpenoid glycoside (dalsaxin) isolated from the root of D. saxatilis was investigated by in vitro methods in the rat. Dalsaxin caused a dose-related increase in uterine muscle contraction. The contraction was single and transient and was abolished by moderate doses of isoprenaline (1.80 nmol-0.40 mumol) and salbutamol (0.13-25 mumol). Adrenaline (9.10 nmol) also caused a reversible decrease (92.6%; P < 0.01) in myometrial contraction stimulated by this glycoside (0.24 mg/ml). Uterine muscle responses to dalsaxin (0.24 mg/ml) were enhanced by the beta-adrenergic receptor antagonist, propranolol, in a dose related manner. Atipamezole (1.50 ng/ml) but not prazosin (7.72 nmol-15.60 nmol) substantially reduced (80%; P < 0.01) myometrial contractions induced by this uterine spasmogen. The results suggest that dalsaxin enhances uterine muscle contraction by stimulating post junctional alpha 2-adrenergic receptors, presumably by inhibiting plasma membrane adenylate cyclase system and its associated increase in intracellular cAMP content.

Renin-like activity in the rat epididymis.

'Whole' cauda epididymal homogenate and individual components of the cauda epididymis viz, cauda epididymal cells, epididymal plasma and sperm cells, as well as the blood plasma of the rat were screened for renin-like activity by in vivo method. Enzyme activity was high in 'whole' cauda epididymal homogenate, but very low in blood plasma. Evaluation of individual components of the epididymis revealed a relatively high enzyme activity in the epididymal cells but low activity in epididymal plasma and epididymal sperm cells. The high activity in epididymal cells was not affected by efferent duct ligation for 8 weeks and bilateral nephrectomy. Like most other epididymal functions, renin-like activity in the epididymis was androgen dependent. It was concluded that cauda epididymis of the rat contains the enzyme renin, whose activities may be predominantly intracellular.