Plasma Prolactin Concentration Increases after Hypercapnia Acidosis

Abstract

Responses of plasma prolactin (PRL) concentration to alterations in carbon dioxide pressure (pCO₂) induced by 4 min of rebreathing out of a bag with 6 l gas initially containing a concentration of 93 % O₂ and 7 % CO₂ (hypercapnia hyperoxia; HH) and 4 min of voluntary hyperventilation (VH) at a respiratory rate of 28 - 32 per minute were investigated in ten males. During rebreathing in HH, an augmentation of pCO₂ from 40.2 ± 2.1 to 63.7 ± 5.4 mmHg and a decrease of pH from 7.4 ± 0.02 to 7.32 ± 0.04 were found in capillary blood (p < 0.01). Neither breathing frequency (BF) nor plasma PRL changed during this period. After two minutes of post-rebreathing, pCO₂ and pH returned to basal values. BF increased from 2 min of rebreathing (12.4 ± 1.9 breath/min) until 11 min of recovery period (18.1 ± 4.9 breath/min) (p < 0.01), while plasma PRL increased from end of rebreathing (11.59 ± 1.49 ng/dl) to 11 min of recovery period (13.63 ± 1.97 ng/dl) (p < 0.01). In VH, hyperventilation decreased pCO₂ from 39.91 ± 2.62 to 21.73 ± 2.59 mmHg (p < 0.01) and increased pH from 7.39 ± 0.04 to 7.58 ± 0.04 (p < 0.01) in capillary blood. After four minutes of recovery from hyperventilation, pH and pCO₂ were back to their basal values. No changes in plasma PRL were found throughout VH. This present pilot study’s new finding is that plasma PRL increases after hypercapnia acidosis. This indicates that acidosis-induced central chemoreflex function increases phrenic nerve activity based on serotonergic modulation, leading to an augmentation of BF. As serotonin is also the main PRL-releasing factor, this might have had the collateral effect of causing PRL release and delayed appearance in the peripheral circulation.

Prolactin · Acidosis · Hyperventilation · Serotonin · Chemosensitivity

References

• 1 Vesely D L, San Miguel G I, Hassan I, Schocken D D. Atrial natriuretic hormone, vessel dilator, long acting natriuretic hormone, and kaliuretic hormone decrease circulatioing prolactin concentrations.  Horm Metab Res. 2002;  34 245-249
• 2 Yen S SC. Prolactin in human reproduction. In: Yen SSC, Jaffe RB (eds) Reproductive endocrinology. Physiology, pathophysiology and clinical management. Philadelphia; Saunders 1991: 357-388
• 3 Mallmann E S, Ribeiro M FM, Spritzer P M. Effect of serotonin depletion by p-chlorophenylalanine on serum prolactin levels in estrogen-treated ovariectomized rats: insights concerning the serotoninergic, dopaminergic and opioid systems.  Horm Metab Res. 2001;  33 337-342
• 4 Tuomisto J, Manisto P. Neurotransmitter regulation of anterior pituitary hormones.  Pharmacol Rev. 1985;  37 249-332
• 5 Clemens J A, Roush M E, Fuller R W. Evidence that serotonin neurones stimulate secretion of prolactin releasing factor.  Life Sci. 1978;  22 2209-2213
• 6 Strüder H K, Weicker H. Physiology and pathophysiology of the serotonergic system and its implications on mental and physical performance. Part. I.  Int J Sport Med. 2001;  22 467-481
• 7 Bonham A C. Neurotransmitter in the CNS control of breathing.  Resp Physiol. 1995;  101 219-230
• 8 Wang W, Pizzonia J H, Richerson G B. Chemosensivity of rat medullary raphe neurones in primary tissue culture.  J Physiol (Lond). 1998;  551 433-450
• 9 Wang W, Tiwari J K, Bradley S R, Zaykin A V, Richerson G B. Acidosis-stimulated neurones of the medullary raphe are serotonergic.  J Neurophysiol. 2001;  85 2224-2235
• 10 Read D JC. A clinical method for assesing the ventilatory response to carbon dioxide.  Aust Ann Med. 1967;  16 20-32
• 11 Ursino M, Magosso E, Avanzolini G. An integrated model of the human ventilatory control system: the response to hypercapnia.  Clin Physiol. 2001;  21 447-464
• 12 Pilowsky P M, De Castro D, Llewellyn-Smith I, Lipski J, Voss M D. Serotonin immunoreactive boutons make synapses with feline motoneurones.  J Neurosci. 1990;  10 1091-1098
• 13 Holtman J R Jr.. Immunohistochemical localization of serotonin- and substance P-containing fibers around respiratory muscle motoneurones in the nucleus ambiguous of the cat.  Neurosci. 1988;  26 169-178
• 14 Voss M D, De Castro D, Lipski J, Pilowsky P M, Jiang C. Serotonin immunoreactive boutons form close appositions with respiratory neurones of the dorsal respiratory group in the cat.  J Comparative Neurology. 1990;  295 208-218
• 15 Bainton C R, Kirkwood P A. The effect of carbon dioxide on the tonic and the rhythmic discharges of expiratory bulbospinal neurones.  J Physiol. 1979;  296 291-314
• 16 Mueller R A, Towle A C, Breese G R. Supersensitivity to the respiratory stimulatory effect of TRH in 5,7-dihydroxytryptamine-treated rats.  Brain Research. 1984;  298 370-373
• 17 Veasey S C, Fornal C A, Metzler C W, Jacobs B L. Single-unit responses of serotonergic dorsal raphe neurones to specific motor challenges in freely moving cats.  Neurosicences. 1997;  79 161-169
• 18 Freeman M E, Kanyicska B, Lerant A, Nagy G. Prolactin: Structure, function and regulation of secretion.  Physiol Rev. 2000;  80 1523-1631
• 19 Ahmad H R, Loeschcke H H. Fast bicarbonate-chloride exchange between brain cells and brain extracellular fluid in respiratory acidosis.  Pflügers Arch. 1982;  395 293-299
• 20 Maren T H. Effect of varying CO₂ equilibria on rates of HCO₃ formation in cerebrospinal fluid.  J Appl Physiol. 1979;  47 471-477
• 21 Nicoll C S. Physiological actions of prolactin. In: Knobil E, Sawyer NH (eds) Endocrinology. Handbook of physiology. Am. Physiol. Soc 1974 sect. 7, vol. 1, pt. II: 253
• 22 Foskett J K, Bern H A, Machen T E, Conner M. Chloride cells and the hormonal control of teleost fish osmoregulation.  J Exp Biol. 1983;  106 255
• 23 Robertson M, Boyajian M, Patterson K, Robertson W. Modulation of the chloride concentration of human sweat by prolactin.  Endocrinology. 1986;  119 2439-2444
• 24 Thompsom S A. Localization of immunoreactive prolactin in ependyma and circumventricular organs of rat brain.  Cell Tissue Res. 1982;  225 79-93
• 25 Lai Z, Roos P, Olsson Y, Larsson C, Nyberg F. Characterization of prolactin receptors in human choroid plexus.  Neuroendocrinology. 1992;  56 225-233
• 26 Mangurian L P, Jurjus A R, Walsh R J. Prolactin receptor localization to the area postrema.  Brain Res. 1999;  836 218-220
• 27 Douglas R M, Trouth C O, James S D, Sexcius L M, Kc P, Dehkordi O, Valladares E R, Mckenzie C. Decreased CSF pH at ventral brain stem induced widespread c-Fos immunoreactivity in rat brain neurones.  J App Physiol. 2001;  90 475-485
• 28 Smith Q R, Johanson C E. Active transport of chloride by lateral ventricle choroid plexus of the rat.  Am J Physiol. 1985;  249 F470-F477
• 29 Strüder H K, Hollmann W, Weicker H, Schiffer T, Weber K. Blood oxygen pressure affects plasma prolactin concentration in humans.  Acta Physiol Scand. 1999;  165 265-271