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A sarcoplasmic calcium-binding protein (SCP) has been purified from the muscle of the protochordate Amphioxus and shown to be more similar to invertebrate SCP's than to their counterpart found in vertebrates, i.e. parvalbumins. The Amphioxus protein has a pI of 4.9, is rich in tyrosine and tryptophan, has a molecular weight of 22,000 and binds strongly 2Ca2+ with a pK of 7.88. Magnesium competes with calcium for only one of the two metal-binding sites and induces positive cooperativity in Ca2+ binding. In cyclostome muscle (lamprey and hagfish), no protein with high affinity for Ca2+ or Mg2+ could be found, irrespective of molecular weight. Instead, a protein with moderate affinity for Ca2+ (less than or equal to 10(5) M(-1)) was detected: it has a molecular weight of 60,000 and might be quite ubiquitous, as the presence of a similar protein has been reported both in red and white muscle of vertebrates such as chicken and rabbit.

I.v. injection of 40 mg/kg or 65 mg/kg streptozotocin reliably induced diabetes in female Sprague-Dawley rats, but failed to induced hypertension within the following 42 days. In most animals injected with the higher dose and in some animals injected with the lower dose the tail blood flow was permanently impaired so that no blood pressure signals could be obtained by tail plethysmography. This phenomenon occurred also when the drug was injected into the jugular vein and thus was not due to a local effect of streptozotocin. 15 days after 65 mg/kg streptozotocin, the mean arterial pressure of the rats was similar to that of controls, when measured inthe awake state (carotid cannula) or under ether anaesthesia. 42 days after streptozotocin, under pentobarbital anaesthesia, the blood pressure was again normal in the animals given 40 mg/kg of the drug and depressed in the animals given 65 mg/kg of the drug 42 days previously. The increase of blood pressure induced by 1 microgram/kg (-)-noradrenaline i.v. was similar in the latter group of animals and in controls. The renal cortical renin concentration was much lower than in controls 42 days after either dose of streptozotocin, while the plasma renin activity was normal (40 mg/kg) or increased 65 mg/kg). The low renal renin content may have been due to the diabetic state, rather than to the drug itself. Adrenal medullary dopamine-beta-hydroxylase activity was increased 42 days after the higher dose of streptozotocin.

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