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A simple and accurate method is described for the quantitative determination of alkaline phosphatase in tissue homogenates, utilizing stable buffered phenolphthalein monophosphate as substrate. The compound, which is hydrolyzed at a rate linear to enzyme concentration and incubation time, provides a chromogen directly for spectrophotometric determination. The assay does not require the addition of a non-specific protein or Mg++ for optimal activity and is equally reactive in glass and plastic flasks. The technique affords good sensitivity by measuring enzyme activity in homogenates as dilute as 0.0005% (small intestine). Quadruplicate determinations varied <1%. Small intestine was the most reactive of the rat organs tested, followed by the kidney, lung, heart and spleen.

Serum immunoreactive relaxin levels and ripening of the cervix were measured throughout pregnancy in hamsters. RIA relaxin rose from an undetectable level on day 7 to a maximum value of 29 ng/ml on day 15 of gestation and then fell prior to parturition. The cervix became progressively more dilatable from the 12th to the 16th day of pregnancy. It is suggested that the endogenous relaxin measured by RIA may induce the cervical softening. The absolute levels of immunoreactive relaxin appear to be 10 to 15-fold higher than those previously observed in rats, mice and guinea pigs.