LACK OF RISE IN SERUM PROLACTIN FOLLOWING YTTRIUM‐90 INTERSTITIAL IRRADIATION FOR ACROMEGALY

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Abstract
The possibility was investigated that the increase in serum PRL [prolactin] levels observed in patients with acromegaly treated with external irradiation could be due to damage to the hypothalamus or portal vessels, by comparing the effects of yttrium-90 interstitial irradiation, which is highly localized and does not normally extend to the hypothalamus, in a similar series of patients. Sixteen acromegalic patients treated by interstitial irradiation with yttrium-90 are described; growth hormone fell from a mean of 131 mU/l (median 113 mU/l) to 17 mU/l (median 8 mU/l) after 1 yr (P < 0.001). PRL fell in the 5 initially hyperprolactinemic patients (mean fall .+-. SD: 39 .+-. 17 .mu.g/l at 1 yr), but remained unchanged in the normoprolactinemic group; PRL responsiveness to TRH was retained. Five, out of the 7 normoprolactinemic patients examined, were shown by in vitro studies of their pituitary biopsies to have tumors that also synthesized or secreted PRL. The rise in PRL following external irradiation apparently is the result of damage to the hypothalamus or portal vessels. A less likely explanation is that an overgrowth of radio-resistant PRL-secreting tumor cells is occurring after external irradiation, but not after yttrium-90 implantation.