690 



PHYSIOLOGY OF GONADS 



fetuses gain. But it is also important to 

 recall that there is a shift in protein, because 

 its distribution in organs of pregnant rats 

 differs from that in nonpregnant animals 

 (Poo, Lew and Addis, 1939). Other changes 

 in the maternal organism were enumerated 

 b}^ Newton (1952) and by Souders and 

 Morgan (1957). 



A measure of nitrogen balance during 

 pregnancy, rather than weight of young at 

 birth, has been suggested as a means of 

 determining a diet adequate for reproduc- 

 tion (Pike, Suder and Ross, 1954). After 

 the 15th day, a retention of body protein 

 increases, blood amino nitrogen and amino 

 acids decrease, and urea formation de- 

 creases. These metabolic activities suggest 

 an increase in growth hormone although the 

 levels of this hormone have not been esti- 

 mated (Beaton, Ryu and McHenry, 1955). 

 Placental secretions have also been asso- 

 ciated with the active anabolic state of the 

 second half of pregnancy, because removal 

 of the fetuses in the rat did not change the 

 anabolic activity, whereas removal of the 

 placentas was followed by a return to nor- 

 mal (Bourdel, 1957). A sharp increase in 

 liver ribose nucleic acid has been observed 

 during late pregnancy in mice and rats and 

 the effect attributed to a placental secretion 

 or to estrogen. Species differences also in- 

 fluence the results because only a modest 

 change in liver RNA was observed in guinea 

 pigs and no change occurred in cats (Camp- 

 bell and Kostcrlitz, 1953; Campbell, Innes 

 and Kosterlitz, 1953a, b). 



Clinical observations have related both 



TABLE 12.10 



Nutrition and pregnancy in rats 



(From J. H. Leathern, in Recent Progress in 



the Endocrinology of Reproduction, Academic 



Press, Inc., New York, 1959.) 



toxemia of pregnancy (Pequignot, 1956) 

 and prematurity to inadequate nutrition 

 (Jeans, Smith and Stearns, 1955). The po- 

 tential role of protein deprivation in the 

 pathogenesis of the toxemia of pregnancy 

 prompted studies in sheep and rats. In sheep 

 nutritionally induced toxemia simulates the 

 spontaneous toxemia (Parry and Taylor, 

 1956), but only certain aspects of toxemia 

 were observed in the pregnant rat subjected 

 to low protein diets. When rats were fed 5 

 per cent casein and mated, fluid retention 

 was observed (Shipley, Chudzik, Curtiss 

 and Price, 1953) and pregnancy was com- 

 pleted in only 48 per cent of the animals 

 Curtiss, 1953). Gain in body weight in the 

 adult rat and gain in fetal weight were sub- 

 normal as the result of a low protein feeding 

 during pregnancy. 



Complete removal of protein from the 

 diet beginning at the time of mating did not 

 prevent implantation but did induce an 86 

 to 100 per cent embryonic loss. The effect 

 was not related solely to food intake (Nel- 

 son and Evans, 1953) , as we will see in what 

 follows when the relationship between pro- 

 tein deficiency and the supply of estrogen 

 and progesterone is described. Limiting pro- 

 tein deprivation to the first 9 to 10 days of 

 pregnancy will also terminate a pregnancy, 

 but when the protein was removed from the 

 diet during only the last week of pregnancy, 

 the maternal weight decreased without an 

 effect on fetal or placental weight (Camp- 

 bell and Kosterlitz, 1953). As would be an- 

 ticipated, a successful pregnancy requires 

 protein of good nutritional quality and the 

 caloric intake must be adequate. Thus, an 

 18 per cent gelatin diet failed to maintain 

 pregnancy when 200 calories per kilogram 

 were fed, whereas a similar level of casein 

 was adequate (Table 12.10). However, re- 

 ducing caloric intake to 100 calories despite 

 an otherwise adequate protein ration in- 

 fluenced the number and size of fetuses 

 (Leathern, 1959b). Additional proteins 

 should be studied and related to biochemi- 

 cal changes in pregnancy and to the need for 

 specific amino acids; for example, elimina- 

 tion of methionine or tryptophan from the 

 diet may or may not be followed by resorp- 

 tion (Sims, 1951; Kemeny, Handel, Kertesz 

 and Sos, 1953; Albanese, Randall and Holt, 

 1943). Excretion of 10 amino acids was in- 



