SEQUENTIAL AND ULTRASTRUCTURAL-STUDY OF M URINE LACTOTROPIC RESPONSE TO STRESS IN REACTION TO AGE

In adult rats, ether inhalation stress stimulated basal serum prolacti n (PRL) significantly, within a maximum delay of one minute. The same pattern was seen with immature animals of 15-20 and 30 days of age. In contrast, in 2 or 6 days old neonates, serum PRL concentrations remai ned unaffected by stress. This lack of responsiveness suggests the exi stence of a transient impairment of lactotroph hormones to stressful s timuli during postnatal life. This hypothesis has been controled by ul trastructural exploration of lactotrophs. The distribution of organite s and secretion grains in lactotrophs was similar in unstressed neonat es and adult rats, but after ether stress, the distribution of secreti on grains become different with age. Adult lactotrophs showed a periph eral secretion grains aspects indicating cells discharge. In the very young rats, the grains were distributed in the totality of the cytopla sm. These results confirm the existence, in the lactotrophs, of a refr actory period to stress in the neonate rats.