Growth hormone (GH) and
prolactin share similarities in structure and function. We have previously shown that women with congenital
isolated GH deficiency (IGHD) caused by a homozygous mutation in the
GHRH receptor gene (GHRHR) (MUT/MUT) have a short reproductive life, with anticipated climacteric. At climacteric, they have lower
prolactin levels than normal controls (N/N). Because they are able to breast feed, we hypothesized that this
prolactin reduction is limited to climacteric, as result of lower
estradiol exposure of the lactotrophs. The purposes of this work were to assess
prolactin levels in broader age adults homozygous and heterozygous (MUT/N) for the mutation and in normal controls (N/N), and to correlate them to sex
steroids levels. We enrolled 24 GH-naïve MUT/MUT (12 female), 25 MUT/N (14 female), and 25 N/N (11 female) subjects, aged 25-65 years. Anthropometric data and serum
prolactin,
estradiol, total
testosterone, and
sex hormone binding globulin (SHBG) were measured. Free
testosterone was calculated.
Prolactin levels were similar in the three groups. In males,
testosterone and SHBG levels were higher in MUT/MUT in comparison to N/N. There was no difference in free
testosterone among groups. In all 74 individuals,
prolactin correlated inversely with age (p < 0.0001) and directly with serum
estradiol (p = 0.018).
Prolactin levels in subjects with IGHD due to a homozygous GHRHR mutation are similar to heterozygous and normal homozygous, but total
testosterone and SHBG are higher in male MUT/MUT, with no difference in free
testosterone. The reduced
prolactin level is limited to climacteric period, possibly due to reduced
estrogen exposure.