Short-term Physiological Changes Research Articles

Cholesterol oxidation in primates by simultaneous sterol balance and breath analysis.

Six female adult rhesus monkeys and baboons with exteriorized enterohepatic circulations were simultaneously assessed following [26-14C]cholesterol pulse labeling by 14CO2 breath analysis and combined isotopic and chromatographic sterol balance during metabolic steady state. Bile acid synthesis and/or secretion were compared with 14CO2 breath analysis of cholesterol oxidation during short term physiological changes, and with total bile acid diversion and feedback inhibition, and biliary tract obstruction. Cholesterol oxidation by breath analysis compared closely with acidic sterol losses during steady-state conditions (145.6 +/- 23.9 vs 144.6 +/- 24.4 mg/24 h) and was sensitive enough to detect changes resulting from diurnal variation and fasting. The 14CO2 test detected inhibition of bile acid synthesis consequent to bile acid feedback (355 +/- 32 to 88 +/- 31 mg/24 h, P less than 0.001) or biliary tract obstruction (158 +/- 27 to 60 +/- 28 mg/24 h, P less than 0.05) but underestimated increased synthesis induced by acute bile diversion (245 +/- 24 vs. 868 +/- 104 mg/24 h, P less than 0.01 at 24 h). Insignificant 14C was detected by carcass analysis following cessation of exhaled 14CO2.

CATEGORIES OF ADAPTATION

Two categories of adaptations are generally recognised. Fixed adaptations are determined in individual by innate factors independently of its particular environmental circumstances. Facultative adaptations, sometimes called accommodations, arise in individual in response to particular environmental circumstances. Medawar (1951) well illustrates distinction by comparing callosities on hands of a gardener, the response of an individual's tissues to irritation, with thickening on soles of gardener's feet, the response of a genetically cdiverse population to factors which, by pronmoting survival of some variant formis rather than others, allot them different fractions of ancestry of future generations. Facultative adaptations correspond to AVaddington's (1953b) category of exogenous adaptations. Those fixed adaptations which resemble facultative adaptations (as thickening on soles of gardener's feet) form Waddington's pseudoexogenous category. The remaining fixed adaptations form Waddingtonl's endogenous category. A capacity to form callosities is a general property of terrestrial vertebrate skin. Stated in an alternative form vertebrate skin possesses a callosity forming competence. The realisation of callosity formiing competence of palms of gardener's hanlds is induced by pressure and friction of spade which lhe handles. The realisation of callosity forming competence of soles of gardener's feet is due to some inductive element in pedal morphogenetic field of embryo. Stated thus contrast is less striking. The capacity to form a cornea is another competence of vertebrate skin. That any external factor should directly induce realisation of this competence would have no adaptive significance; it would not, for example, be useful simply that skin should be transparent where light fell upon it without relation to underlying photoreceptors. The presence of an eye-cup leads to realisation of cornea-forming competence. This arrangement works very well in practice and ensures that cornea develops where and only where it is useful. After a certain stage of development this competence is lost. There is a type of adaptation which is sometimes difficult to place. A good example is dermal colour change of amphibians in response to environmental conditions. The colour of skin is influenced by external conditions. Darkening under one set of conditions, paling under another set might be regarded as facultative adaptation. These changes are however normal short term physiological changes. The conditions to which adjustment is made vary as normally in life of individual as night alternates with day. The capacity for change should in this case be regarded as a fixed adaptation. Cases can be imnagined in which it would be more difficult to make a clear decision. Waddington discusses a type of facultative adaptation which is very poorly understood, exemplified by enlargement of one kidney following removal of other or thinning of branchial epithelium of a tadpole reared in water deficient in oxygen. Perhaps this could more fruitfully be regarded as an extension of embryonic regtulation.