Vasotocin-sensitive adenylate cyclase in frog glomeruli

Area of Science:

• * Endocrinology
• * Comparative Physiology
• * Molecular Pharmacology

Background:

• * Neurohypophyseal hormones regulate kidney function in vertebrates.
• * Adenylate cyclase is a key enzyme in cellular signaling pathways.
• * Understanding hormone-receptor interactions in amphibian kidneys is crucial for comparative studies.

Purpose of the Study:

• * To investigate the effect of neurohypophyseal hormones on adenylate cyclase activity in frog kidney segments.
• * To characterize the pharmacological properties of vasotocin receptors in frog glomeruli.
• * To compare these receptors with known vasopressin receptors in mammals and amphibians.

Main Methods:

• * Microdissection of nephron segments from Rana ridibunda kidneys.
• * Enzymatic assays of adenylate cyclase activity in isolated glomeruli and microdissected tubules.
• * Pharmacological characterization using various neurohypophyseal hormone analogs and antagonists.

Main Results:

• * Vasotocin increased adenylate cyclase activity in glomeruli and collecting ducts, but not in proximal or distal tubules.
• * Hormonal stimulation in glomeruli primarily decreased the Km of adenylate cyclase, indicating increased substrate affinity.
• * A distinct rank order of affinity for frog glomerular receptors was observed, differing from mammalian V2 receptors.

Conclusions:

• * Frog glomerular adenylate cyclase is sensitive to specific neurohypophyseal hormones, notably vasotocin.
• * The vasotocin receptors involved exhibit unique pharmacological characteristics.
• * These receptors differ from both mammalian V2 vasopressin receptors and amphibian V2-like receptors in other tissues.