Metabolic Body Weight Basis Research Articles

A note on the effect of ageing on whole-body protein turn-over in goats

In ruminants a dynamic state of protein turn-over has been poorly understood although the methodology of measuring the rate of protein turn-over has recently been advanced to a great extent (Waterlow, Garlick and Millward, 1978). Available evidence suggests that ruminants such as sheep and cows are no exception among various mammalian species when whole-body protein synthesis of adult animals is compared on a metabolic body-weight basis (Waterlow et al., 1978; Reeds and Lobley, 1980).

Effect of Age and Protein Restriction on the Clearance and Secretion of Growth Hormone in the Domestic Fowl

Metabolic clearance rates (MCR) and secretion rates for growth hormone (GH) were determined in young (6-wk-old) chicks and adults (1 yr old) as well as in chicks fed low protein diets for 2 wk. Birds were either conscious or anesthetized during these determinations in the latter study. Age-related differences in plasma concentrations of GH reflect greater secretion of GH in younger chicks (3.5-fold increase). The MCR was reduced by 35% in chicks compared with adults, but when expressed per unit metabolic body weight, was higher in the young chickens. The MCR in protein-restricted chicks was 28% lower than in that of controls. However, when the MCR was calculated on a metabolic body weight basis, protein-restricted and control chicks did not differ in MCR. Elevated plasma concentrations of GH in unanesthetized, protein-restricted chicks were due to greater GH secretion (2.4-fold) of these chicks compared with secretions of chicks fed control diets. Basal secretions of GH, determined in the anesthetized chicks, did not differ between dietary treatments. These results indicate that secretion of GH but not clearance was affected by protein restriction in conscious birds.

Metabolic clearance rate of rat prolactin in preweanling rat pups.

The metabolic clearance rate (MCR) of immunoreactive rat prolactin (rPRL) was determined in urethane-anaesthetized 14 to 16-day-old rat pups using the constant infusion to equilibrium method. Two different doses of rPRL were used, 329 and 472 ng/min each at a volume of 0.0025 ml/min for 30 min. The MCR was 0.216 ml/min following infusion of 329 ng PRL/min dose and 0.337 ml/min following infusion of the 472-ng/min dose. When calculated on the basis of metabolic body weight the MCR of rPRL in rat pups was comparable to that of adult rats.

Comparison of Heat Production of Chickens Measured by Energy Balance and by Gaseous Exchange

An open-circuit respiration calorimeter suitable for chickens or other small animals has been constructed. The system contains two animal chambers and is capable of determining heat production of two animals or groups of animals independently and simultaneously with gas collection apparatus for continuous sampling of chamber gases. The operation of the system was tested in two experiments by determining heat production of two groups of 10-week-old, full-fed cockerels over a 4-day period both by energy retention (body balance) and gaseous exchange. Heat production (kilocalories per bird per 24 hours) as determined by energy balance versus gaseous exchange was 359 versus 348 in one experiment and 395 versus 393 in the other. The agreement was sufficiently close to support the use of respiration calorimetry to measure heat production of chickens under experimental conditions in this laboratory without killing the experimental subjects. On the basis of metabolic body weight (in kilograms, W0.75) heat production measured in this manner was 161 and 173 kcal (day · W0.75) in experiments 1 and 2, respectively.