The developing pituitary is a rapidly changing environment that is constantly meeting the physiological demands of the growing organism. During early postnatal development, the anterior pituitary is refining patterns of anterior hormone secretion in response to numerous genetic factors. Our laboratory previously developed a somatotrope leptin receptor (LEPR) deletion mouse model that had decreased lean body mass, disrupted metabolism, decreased GH stores and was GH deficient as an adult. To understand how deletion of LEPR in somatotropes altered GH, we turned our attention to postnatal development. The current study examines GH, PRL, TSH, ACTH, LH and FSH secretion during postnatal days 4, 5, 8, 10 and 15 and compares age and sex differences. The LEPR mutants have dysregulation of GH (P < 0.03) and a reduced developmental prolactin peak in males (P < 0.04) and females (P < 0.002). There were no differences in weight between groups, and the postnatal leptin surge appeared to be normal. Percentages of immunolabeled GH cells were reduced in mutants compared with controls in all age groups by 35–61% in males and 41–44% in females. In addition, we measured pituitary expression of pituitary transcription factors, POU1F1 and PROP1. POU1F1 was reduced in mutant females at PND 10 (P < 0.009) and PND 15 (P < 0.02) but increased in males at PND 10 (P < 0.01). PROP1 was unchanged in female mutants but showed developmental increases at PND 5 (P < 0.02) and PND 15 (P < 0.01). These studies show that the dysfunction caused by LEPR deletion in somatotropes begins as early as neonatal development and involves developing GH and prolactin cells (somatolactotropes).
Melody L Allensworth-James, Angela Odle, Anessa Haney, Melanie MacNicol, Angus MacNicol, and Gwen Childs
Tiffany K Miles, Ana Rita Silva Moreira, Melody L Allensworth-James, Angela K Odle, Anessa C Haney, Angus M MacNicol, Melanie C MacNicol, and Gwen V Childs
Anterior pituitary somatotropes are important metabolic sensors responding to leptin by secreting growth hormone (GH). However, reduced leptin signals caused by fasting have not always correlated with reduced serum GH. Reports show that fasting may stimulate or reduce GH secretion, depending on the species. Mechanisms underlying these distinct somatotrope responses to fasting remain unknown. To define the somatotrope response to decreased leptin signaling we examined markers of somatotrope function over different time periods of fasting. Male mice were fasted for 24 and 48 h, with female mice fasted for 24 h compared to fed controls ad libitum. Body weight and serum glucose were reduced in both males and females, but, unexpectedly, serum leptin was reduced only in males. Furthermore, in males, serum GH levels showed a biphasic response with significant reductions at 24 h followed by a significant rise at 48 h, which coincided with the rise in serum ghrelin levels. In contrast, females showed an increase in serum GH at 24 h. We then explored mechanisms underlying the differential somatotrope responses seen in males and observed that pituitary levels of Gh mRNA increased, with no distinction between acute and prolonged fasting. By contrast, the Ghrhr mRNA (encoding GH releasing hormone receptor) and the Ghsr mRNA (encoding the ghrelin receptor) were both greatly increased at prolonged fasting times coincident with increased serum GH. These findings show sex differences in the somatotrope and adipocyte responses to fasting and support an adaptive role for somatotropes in males in response to multiple metabolic signals.