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Effect of Suckling upon the Secretion and Release of Prolactin from the Pituitary of the Lactating Rat¹

University of Tennessee, ³ Memphis 37901 and Instituto de Investigaciones Biomedicas Universidad Nacional Autonoma de México, México, D.F.

Abstract

There are several factors which experimental data indicate influence pituitary prolactin release and reaccumulation (figure 13). There are additional factors which have been suggested—but with little or no supportive data—also to influence the same functions of the pituitary, thus:

1. The extent of the release of prolactin is influenced by:
   1. Suckling strength.
      
   2. Previous non-suckling interval.
      
   
   
2. The extent of the post-suckling reaccumulation of prolactin is influenced by:
   1. Suckling strength.
      
   2. Previous non-suckling interval.
      
   
   
3. The mechanism of prolactin release by suckling involves the hypothalamus possibly by means of:
   1. Neurons which tonically discharge a prolactin-release-inhibiting-factor (PRIF).
      
   2. Neurons which have an adrenergic component.
      
   3. Neurons which exhibit a fairly long refractory period.
      
   4. Neurons which elaborate a prolactin-releasing-factor (PRF).
      
   
   
4. The mechanism of the post-suckling re-accumulation of prolactin by the pituitary probably involves:
   1. Hypothalamic neurons which elaborate a "prolactin-synthesis-stimulating-factor" which, in turn, may be sensitive to the postsuckling circulating level of prolactin.
      
   2. Inhibition of further release via:
      1. Neural refractoriness of the prolactin release mechanism.
         
      2. Resumption of PRIF secretion.
         
      3. Exhaustion of PRF.
         
      4. Exhaustion of "mature" prolactin.
         
      
      
   
   

¹ Supported by U.S.P.H.S. Grant 03637.

² Research Career Development Awardee of the U.S.P.H.S.

³ Department of Physiology and Biophysics.