Journal of Endocrinology · 1978 · 24 citations · 0 references
MedicineEndocrinologyPhysiologyCircadian RhythmsHormone BiochemistryNeuroendocrinologyCircadian Activity PatternsCircadian EndocrinologyCircadian PhysiologySeasonal EndocrinologyStress EndocrinologyCircadian Endocrine ControlCircadian Hormone RegulationCircadian Regulation Of Pituitary HormonesCircadian Regulation Of ProlactinMale Prolactin PhysiologyPlasma Concentration VariabilityProlactin Circadian RhythmProlactin Rhythms
The occurrence of circadian variations in the concentration of prolactin in the plasma of 6- to 9-month-old male rats has been assessed in animals exposed to light for 14 h/day (lights on 06.00--20.00 h). Blood samples were obtained after decapitation, or from individual rats at regular intervals via a permanent cannula. Care was taken to limit stress during sampling. The concentration of prolactin in the plasma was significantly lower between 07.00 and 15.00 h than at other times. Between 15.00 and 20.00 h (during the light period), the concentration of prolactin was significantly higher in comparison with the preceding period, or with the remainder of the 24 h period. During the night, the concentration fluctuated, probably because of episodic releases of the hormone. The possible physiological significance of a circadian rhythm in the plasma concentration of prolactin and the implications for endocrine experimentation are discussed briefly.