Prolactin Regulates Seasonal Changes in Water Rheostasis in Siberian Hamsters (Phodopus sungorus)
Prolactin (PRL) is a multifunctional hormone involved in diverse physiological processes, including lactation, reproduction, growth, and renal function. However, its effects on kidney morphology in seasonal mammals remain largely unexplored. The Siberian hamster (Phodopus sungorus), a seasonally breeding species, exhibits distinct physiological adaptations in response to photoperiod-driven changes in prolactin levels. Previous studies have demonstrated that PRL treatment significantly increases kidney mass, yet the underlying molecular mechanisms remain unclear. This study aimed to investigate the impact of PRL on kidney morphology and the associated molecular pathways. Histological analysis using Hematoxylin and Eosin (H&E) staining revealed that PRL treatment significantly increased convoluted tubule width (CTW). To elucidate the molecular basis of these morphological changes, transcriptome analysis was performed, identifying 19 significantly enriched pathways that were negatively correlated with CTW. These findings provide novel insights into the role of PRL in regulating seasonal kidney morphology and highlight key molecular pathways involved in this process.Our results contribute to a deeper understanding of PRL's role in renal adaptations to seasonal changes, paving the way for future research into the endocrine regulation of kidney structure and function in seasonal mammals. Overall design: Two experiments were conducted to assess seasonal changes in water rheostasis and the role of prolactin in kidney physiology.  1. Experiment 1: Seasonal Changes in Water Rheostasis Adult male Siberian hamsters (N = 54) were housed under long photoperiod (LP; 16L:8D). A subset (N = 6) remained under LP, while the rest were transferred to short photoperiod (SP; 8L:16D) and euthanized at 4-week intervals (N = 6 per time point, up to 32 weeks). Kidney dimensions were recorded using a vernier caliper, and kidney volume was estimated. Kidneys were weighed and stored at -80°C. 2. Experiment 2: Prolactin's Role in Kidney Physiology Adult female hamsters (N = 12) housed in LP were exposed to SP for 8 weeks and assigned to two groups: control (N = 6; vehicle injections) and prolactin-treated (N = 6; 18 µg PRL daily for 3 days). Injections were administered at mid-light phase. Hamsters were euthanized 2–4 hours after lights-on. Kidney volume and mass were recorded and stored at -80°C for further analysis.Kidney samples from Experiment 1 (LP, SP12wk, SP28wk; N = 4 per group) and Experiment 2 (SAL, PRL; N = 6 per group) underwent transcriptome sequencing. RNA was extracted using the QIAGEN RNeasy Plus Mini Kit, and quality was assessed via Nanodrop ND-1000 (260/280 ~2.0).Oxford Nanopore Direct cDNA Native Barcoding (SQK-DCS109, EXP-NBD104) was used for cDNA synthesis. Sequencing was performed on MinION Mk1B using R9 Spot-ON Flow Cells (FLO-MIN106D), with 12 samples per flow cell. Runs lasted 72 hours at -180 mV, generating fast5 files for downstream analysis.