Circulating blood progesterone is pulsatile throughout the rat oestrous cycle

O. K. Park, V. C. Ramirez

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17 Scopus citations


In the present experiment, we determined circulating progesterone (P4) levels of intact cycling female rats. A cannula constructed from polyethylene-50 tubing containing heparinized saline was inserted into the jugular vein of the rat under light ether anaesthesia and after a 3-6 h recovery period sequential blood samples were withdrawn from unanaesthetized, freely-moving rats. Blood samples (80-100 μl) were collected at 10-min intervals for 6 h and the volume was replaced with saline. Plasma P4 was determined using a specific P4 radioimmunoassay. Four rats in each of three phases of the rat oestrous cycle (E, D1, D2) were examined. In addition, rats in proestrus were diveded into an early (EP, N = 4) and late (LP, N = 4) proestrous conditions. Individual data were analyzed by PULSAR as adapted for an IBM-PC. P4 was found to fluctuate in a pulsatile mode throughout the rat oestrous cycle. Mean levels of circulating P4 were lowest (38.8 ± 1.7 nmol/l plasma) in EP and highest (122.5 ± 1.3) in D1. The frequency of P4 pulses was dramatically decreased in D1 (2.50 ± 0.86 pulses/6 h), whereas no difference was found among the other days of the cycle (7.25 ± 0.47 in E, 7.25 ± 0.85 in D2, 5.75 ± 1.31 in EP, and 6.50 ± 1.04 in LP). Interestingly, the amplitude of P4 pulses was significantly lower in EP (14.0 ± 2.91 pmol), whereas no difference was found among other groups. Another group of experimental animals were ovariectomized (N = 4; two with and two without an implant of a silastic capsule of P4) and similarly bled. These animals demonstrated a fairly stable circulating pattern of P4. The present data demonstrate for the first time that P4 in rat blood fluctuates in a pulsatile manner.

Original languageEnglish
Pages (from-to)121-128
Number of pages8
JournalActa Endocrinologica
Issue number1
StatePublished - 1987

ASJC Scopus subject areas

  • Endocrinology


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