Estimation of protein reserves and the nitrogen content of organs in protein-depleted and repleted cocks

The concept of labile nitrogenous matter in the body which may be mobilized during stress conditions and which has become variously known as protein stores, or reserves, is not new.According to Madden & Whipple (1g40), in 1906 Morawitz demonstrated that, during starvation after severe depletion of plasma proteins through bleeding, plasma proteins were regenerated from what Madden & Whipple believed to be protein stores.Madden & Whipple (1940), who reported on a series of plasmaphaeresis experiments with dogs, concluded that plasma proteins formed 'part of a balanced system of body proteins' in which a 'steady state of ebb and flow exists between it [the plasma proteins] and a portion of the cell and tissue body proteins'.Yuile, Lucas, Neubecker, Cochrane & Whipple ( 1959) have since demonstrated that the drop in plasma proteins of dogs subjected to plasmaphaeresis was smaller than expected, because extravascular protein-building blocks found their way into the plasma proteins.From this observation one might conclude that extravascular proteins may serve as a source of reserve protein drawn upon for the synthesis of plasma proteins under conditions of stress.Fisher (1954) and Mitchell (1962) critically discuss the possible existence of reserve proteins.Both accept the presence in the body of a protein fraction which is readily katabolized when the animal is placed on a diet devoid of nitrogen or is subjected to certain stress conditions.The study of Longenecker & Hause (1958) may be interpreted as suggesting that free amino acids may also serve as protein reserves by making good dietary protein inadequacies.The N excretion of animals on a protein-free diet generally displays a particular pattern.Initially the rate of excretion is rapid, but it gradually declines and becomes constant at a value usually referred to as the endogenous N excretion (Folin, 1905).According to Allison & Wannemacher (1957), the magnitude of reduction in N excretion to this constant value may be considered an estimate of protein reserves.Shapiro & Fisher (1962) have reported the partial repletion of body N stores by non-essential amino acid N in adult cocks depleted to the endogenous level of N excretion.The non-essential amino acids were added to the repletion diet which provided the essential amino acids at levels just adequate for maintenance (Leveille & Fisher, 1958).