THE INVOLVEMENT OF SEROTONIN IN LABOR AND DELIVERY

Proposal for Collaborative Research between Bruce E. Morton, Ph.D, Department of Biochemistry and Biophysics, and X.X. M.D., Department of Obstetrics and Gynecology, University of Hawaii, 2/22/94

BACKGROUND:

Serotonin (5-hydroxytryptamine, 5-HT) is a neurotransmitter, neuromodulator, and neurohormone both in the central nervous system (CNS) and the periphery. It has been found to modulate many behavioral processes through the at least 14 subclasses of its 5-HT receptors. In the periphery, these processes include regulation of the diameter of the vasculature associated with blood-shunting throughout the brain and body. This is illustrated for example in digestion, headache, or in response to wounding.

Serotonin also mediates several important CNS behaviors including the stress response, immune strength, and the predilection for violence toward property, others (homicide), or oneself (suicide). Thus, it is central to the production and treatment of several stress disorders including mania-depression, dysthymia, obsessive compulsive disorder, pre-menstrual syndrome, anorexia-obesity, and several others, such as autism and schizophrenia.

Since the levels of serotonin required to produce its effects are exceedingly small, and great dilutions are involved in brain dialysis and other experimental approaches, it is important to have practical, inexpensive assays of adequate sensitivity. For example, bioassays were once used for example employing the contracture of the rat uterus (!). In the recent past, the inherent fluorescence of the serotonin indole ring derivatives at acid pH was utilized in fluorometric assays of similar sensitivity to the bioassays (>10-8M). These often were not sensitive enough to detect the small amounts of serotonin required to produce its biological effects. More recent serotonin assays have utilized high performance liquid chromatography with electrochemical detection to reach >2x10-10M sensitivity on protein-free samples.

Dr Morton has applied the techniques of the radio-receptor assay on unpurified biological samples to develop an ultrasensitive assay specific for serotonin. It can detect >10-11M serotonin in 100 ul samples (>10 fmoles). This makes it the most sensitive serotonin assay known. With this assay, serotonin concentrations in serum and urine have been measured.

The assay is sufficiently sensitive to make the measurement of salivary serotonin practical for the first time. In the process of learning about human serotonin levels, Dr Morton's group has found that there is a one hour postprandial elevation of serotonin for one hour, possibly associated with the shunting of blood away from the peripheral skeletal muscles to the viscera. Furthermore, they found that several types of stress produce elevations in salivary serotonin. These include heat stress (such as from soaking in very hot baths for 30-60 minutes) and exercise stress (such as from running 30-60 minutes). In experimental animals, if serum serotonin from heat or exercise stress is elevated beyond a certain level, the blood brain barrier (BBB) begins to fail. This leads to heat prostration, exhaustion, altered states of consciousness, and coma by a 5-HT2 receptor mediated process.

In addition, Dr. Morton's group has found that such serotonin-elevating stress leads to rapid (within one hour) down-regulation of central 5-HT2a receptors. It is becoming established that in the CNS, cells bearing 5-HT2a receptors release corticotropin releasing factor (CRF). CRF, not only activates the HPA axis in the periphery, but also binds the locus coeruleus (LC) to produce norepinepherine (NE) release at brain sites causing alarm, temperature elevation, and other elements of sympathetic nervous system activation.

Thus, it is appropriate that after more than one hour of stress the 5-HT2 receptors have been found to be down-regulated, and thus to cease coupling serotonin elevation to CRF release. For example, by about one hour, marathon runners experience "the second wind". It is known that 5-HT2a receptors take 3-5 days to return to their usual sensitivity and CRF-releasing response. This is consistent with the several days of relief from stress (in general) provided by 30-60 minutes of hot tub or exercise stress. Serotonin reuptake inhibitor antidepressants, such as fluoxetine (Prozac), reduce stress ultimately by elevating serotonin to also down-regulate the 5-HT2a receptor subclass.

It is noteworthy that brain serotonin levels are very susceptible to amounts of circulating precursor, tryptophan and also to oxygen availability. Thus, breathing pure oxygen elevates serotonin levels ten fold in rats, and prolonged hyperventilation has been used to produce hallucinosis in humans without the use of hallucinogens. Furthermore, all 5-HT2a receptor agonists are hallucinogens. That is, the hallucinogens act via their ability to mimic the serotonin normally released by stress-inflammation-mediated interleukin-1 at the 5-HT2a receptor.

It has frequently been reported that either low levels of hallucinogens or prolonged hyperventilation cause the appearance of many labor and delivery associated symptoms in humans and animals. These include both rhythmic body thrusting and head pushing, breath-holds, first-breath associated production of copious chords of mucous, neonate type of squalling, and suckling (adult rats). They also produce in adults of either sex a supine posturing with knee-spreading and pelvic movements which can be so vigorous and prolonged as to lead to panting from exertion. This may be followed by a transcendent mental state which may be associated with the uncommon ecstatic acceptance and bonding of the birth pair at delivery. As an added complication, marked (as great as ten fold) individual and perhaps racial differences exist in sensitivity to both antidepressants and hallucinogens.

An earlier proposal along some of these lines was made to your committee by a colleague, now retired from UH and living on the mainland. As you will recall, he proposed to isolate and identify a putative endogenous hallucinogen, which he erroneously proposed to exist and be produced during labor and delivery. As predicted, he failed to find the endogenous hallucinogen. This is because stress elevated endogenous serotonin release at the 5-HT2a receptor is sufficient to account for all these effects without requiring an additional endogenous hallucinogen. However, he was correct that a "birth constellation" of behaviors have been associated with hallucinogen use, if he mentioned this.

HYPOTHESIS:

Based upon the above-mentioned multiple layers of evidence, the following model is proposed: The stress of early labor is predicted to elevate central and peripheral serotonin levels. As serotonin levels rise toward those compromising the blood brain barrier, anciently-evolved placental animal delivery programs are activated in both the mother and the neonate. These lead to the altered mental and physical behaviors associated with active participation in delivery by both the fetus and dam. Not to be overlooked is the known contractile response of the uterus to serotonin itself.

It is further proposed that in the case of prolonged passive labor, or excessively active labor, this process can be controlled by the manipulation of 5-HT2 serotonin tone in the mother. That is, the appropriate use of oxygen or hyperventilation deliberately to raise serotonin tone, and use of antagonists, such as ketanserin, to reduce it. Also to be explored at some point is the possible involvement of serotonin in the respiratory system's transition to air breathing by the fetus.

In addition it is proposed that after one hour of high-stress labor, the 5-HT2 receptors will be down-regulated to produce a "second wind" relief from pain and anxiety. This will allow a satisfactory completion of delivery, and will leave the mother and neonate in positive mental states facilitating bonding.

PROPOSED RESEARCH:

The use of the salivary serotonin assay would provide a relatively simple way to gather new fundamental information on the levels of salivary serotonin present during the various phases of labor.

After first confirming that salivary serotonin is elevated in stage 2 labor, a more complete study could be done. In this, saliva sample collection series on separate patients could be administered as follows:

1. Before labor begins (to establish serotonin baseline.)

2. Latent phase: after 60 seconds of hard uterine contraction.

3. Latent phase: after 5 minutes of relaxation.

4. Early 1st stage: after 60 seconds of hard contraction.

5. Early 1st stage: after 60 seconds of relaxation.

6. Active 1st stage: after 60 seconds of hard contraction.

7. Active 1st stage: after 60 seconds of relaxation.

8. Transition: after 60 seconds of hard contraction.

9. Transition: after 60 seconds of relaxation.

10. 2nd stage: After 30 seconds of pushing.

11. 2nd stage: After 30 seconds of resting.

12. 3rd stage: At delivery of placenta.

13. 3rd stage: 30 minutes after delivery of placenta

14. 3rd stage: 2 hours after delivery of placenta

15. 3rd stage: 6 hours after delivery of placenta

Information required on each patient includes race, age, parity, fetal outcome, and fetal lung maturity.

Based upon the findings of this fundamental study, it is expected that the subsequent course of the research will flow as appropriate. For example, if it is confirmed that salivary serotonin levels are elevated during labor, it would be of interest to compare the regulatory state of 5-HT2 receptors of placenta coming from mothers undergoing intense normal vaginal delivery with those whose placenta was removed after little or no labor by way of cesarian section. It would be important to evaluate the effect upon salivary serotonin of both hyperventilation and breathing oxygen.

Many other possibilities suggest themselves, depending upon the findings of the foregoing proposed research. It may be that this work would justify the later awarding of substantial extramural funding, both to the hospital, the medical school, and the present (and perhaps other) collaborators.