Since the blood and thymus of patients with myasthenia gravis may contain inhibitors of neuromuscular transmission that affect acetylcholine receptors of striated muscle, we used denervated rat muscle to test for inhibitors in 43 serums and 18 thymus glands from such patients. Seven per cent of serums inhibited the binding of 125l alpha-bungarotoxin to triton-solubilized receptors; 65 per cent interfered with binding of toxin-labeled receptors to concanavalin-A coupled to Sepharose gel, and 85 per cent formed IgG-receptor complexes detectable by immunoprecipitation. Serum inhibitory activity varied widely among patients with similar clinical manifestations and was not correlated with duration of myasthenia gravis or thymectomy. Among thymus extracts, 44 per cent were inhibitory in the concanavalin-A binding assay, whereas 72 per cent contained anti-receptor IgG. Thus, serums from patients with myasthenia gravis contain more than one anti-receptor factor.

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Synthetic rat atrial natriuretic peptide (ANP) was examined for effects on guanylate-and on adenylate cyclase activity in ciliary process homogenates and for effects on intraocular pressure in the albino rabbit eye. Ciliary process guanylate cyclase was associated predominantly with the particulate fraction and was partially activated by ANP (EC50, approximately 1 nM) relative to a maximal dose of Na Nitroprusside (2 uM), whereas particulate adenylate cyclase (basal as well as forskolin-stimulated activity) showed no responses to ANP at doses up to 0.3 uM. Particulate cAMP phosphodiesterase activity was stimulated by low doses of cGMP (1-5 uM) in ciliary processes. Thus, ANP, acting via guanylate cyclase, has the potential to regulate phosphodiesterase activity and indirectly decrease cAMP levels in membranes derived from ciliary processes. Intravitreous injection of ANP (2-4 ug/eye) caused a small decrease (1-1.5 mm Hg) in intraocular pressure measured 16-24 hours after injection but the pressure had returned to normal by 40 hours. The findings demonstrate regulation of biochemical and pharmacological responses by ANP in the albino rabbit eye suggesting that this peptide may play a physiological role in secretory functions of ciliary processes.

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