Switch from foetal to adult haemoglobin synthesis in normal and hypophysectomised sheep

Decline with Age in the Rate of Reduction of Progesterone to 20a-Hydroxypregn-4-en-3-one in the Blood of Perinatal Ruminants

“…Adult-type haemoglobin fi-chain synthesis has been detected as early as 120 days gestation in the sheep foetus and represents 100% of de novo synthesis of non-a-chain by term (Wood et al 1976). The few data that have been obtained herein from chronically catheterized sheep foetuses have shown that the decline of 20a-HSD activity begins well prior to parturition, but the timing of this decline has not been fully described and is the subject of further work.…”

“…It was shown that the activity remained constant throughout the last 80 days of gestation but declined to low, adult levels within 6-9 weeks following parturition. Nancarrow and Seamark (1968) suggested that this decline was associated with the replacement of foetal erythrocytes by adult-type erythrocytes, a process which begins around 120-130 days of gestation (Wood et al 1976). Thus the decline in 20IXHSD activity should begin before birth in sheep, cattle and goats but this may not have been detected previously because the particular conditions of incubation allowed the reaction to reach equilibrium.…”

Effect of Hormone-Induced Premature Parturition on Hemoglobin Switching in Sheep

“…The switch from fetal to adult Hb commences approximately Samples were also collected from one fetus or lamb delivered 4 wk before term (142-152 days) and is complete by 170 days prematurely as the result of continuous intravenous infusion of postconception at the latest (1,2,8,9). When the capacity of ovine CRH, 2.4 ~g / h , as reported previously (15).…”

“…It was reported that in lambs carrying the PA gene a small proportion of PC (~1 5 % of total p) appears transiently after birth and persists for several months (10). Many attempts have been made to influence the time of onset of the switch from fetal (7) to adult (P) Hb but these have been largely unsuccessful (8,9,11,12). Once commenced, the rate of the switching process has been shown to be able to be modulated.…”

“…Once commenced, the rate of the switching process has been shown to be able to be modulated. Hypophysectomy or bilateral adrenalectomy of the chronically cannulated fetus causes the completion of the switch to be delayed considerably (8,9). In the adrenalectomized fetus replacement of cortisol in gradually increasing amounts returned the rate of adult Hb synthesis to normal (9).…”