Medical Hypotheses I Mec&zdHyprkrer @ L.qmm
(1991) 36.152-154 Ltd 1991
GmupUK
Artificial Insemination: Can Appropriate Improve Success Rates?
Stimulation
W. G. EBERHARD Smithsonian Tropical Research Institute and Escuela de Biologia, Universitaria, Costa Rica
Universidad
de Costa Rica, Ciudad
Abstract - Studies of other animal species suggest that stimulation during copulation has important effects on the probability of conception. Thus appropriate stimulation during artificial insemination may improve rates of conception.
The male genitalia of many animals not only transfer sperm, but may also induce critical female processes such as sperm transport and implantation which must occur if a copulation is to result in offspring (1, 2). The hypothesis that male genitalia have an ‘internal courtship’ function, which recently rcccived support from a comparative study of primate penis morphology (3), points to the probability that female mammals play important roles, even after copulation has begun, in determining whether their offspring will be sired by any given male (4, 5). This note urges that attempts be made to use this insight from animal studies to improve artilicial insemination techniques in humans. Substantial numbers of human couples arc childless against their will (6), and artificial insemination by donor (AID), a commonly used technique to overcome this problem, is frequently unsuccessful (7, 8). The most common techniques of AID in humans (9, 10) as well as in most domestic mammals (11) do not include attempts to make the stimuli associated with AID resemble those of natural copulations. There are two interesting exceptions. Artificial insemination in Dare received 15 February 1991 Date accepted 23 April 1991
152
mice commonly involves mating the female to a vascctomized male soon after sperm are introduced into her cervix or uterus, or simulating mating with a vaginal tampon (12). Stimuli associated with copulation in mice induce production of progesterone which elicits changes in the uterine lining facilitating implantation (13); numbers of females successfully impregnated by artifcial insemination were more than tripled, and litter sizes nearly doubled by use of an artificial penis and a vaginal tampon (14). Some AID in swine is performed with a pipette with a spiral tip similar to the tip of a boar’s penis; use of such pipettes usually results in less backflow of semen (1.5). In several other mammals stimulation of the female has been shown to increase the chances of reproduction. In rabbits, the number of artificially introduced sperm reaching the Fallopian tubes increased by a factor of four when artificial insemination was folllowed by copulation with a vasectomized male (16). Mechanical distension of the rabbit vagina produces uterine contractions that are probably important in sperm transport (4). In rats, preparation of the uterine lining for implantation and maintenance of the blastocyst is
ARTIACIAL
INSEMINATION
reliably induced by vaginal-cervical stimulation with probes and vibrators (17). The multiple intromissions whilch precede ejaculation in this species, as in some primates (18), promote transcervical sperm transport (19)~; the cumulative stimulatory effect of multiple intromissions can be stored (‘remembered’) by female rats for at least 4 h (20). Male golden hamsters add rcpctitivc intravaginal thrusts during long intromissions late in copulation scquenccs after sperm transfer has already occurred (21); these long intromissions are especially effective in initiating pregnancy, increasing pregnancy rates up to eight times over those resulting from some controls (22). As in other mammals such as goats (23), cattle (24.1, and horses (25). the male genitalia of humans perform complex movements and change form during ejaculation (26). It seems unlikely that such complex and consistent behavior is bereft of reproductive significance. ‘Superoptimal’ patterns of stimuli, which even more effectively increase the probability of the uterus becoming receptive to implantation than does normal male behavior under artiticial conditions, have been found in rats (27). Fertility can also bc affected by general surroundings during artificial insemination. For instance, pregnancy is less likely to result when AID in sheep is pcrfomtcd in the presence of distracting stimuli such as unfamiliar surroundings or barking dogs (28). Coinclusion
if
(1991) 36.152-154 Ltd 1991
GmupUK
Artificial Insemination: Can Appropriate Improve Success Rates?
Stimulation
W. G. EBERHARD Smithsonian Tropical Research Institute and Escuela de Biologia, Universitaria, Costa Rica
Universidad
de Costa Rica, Ciudad
Abstract - Studies of other animal species suggest that stimulation during copulation has important effects on the probability of conception. Thus appropriate stimulation during artificial insemination may improve rates of conception.
The male genitalia of many animals not only transfer sperm, but may also induce critical female processes such as sperm transport and implantation which must occur if a copulation is to result in offspring (1, 2). The hypothesis that male genitalia have an ‘internal courtship’ function, which recently rcccived support from a comparative study of primate penis morphology (3), points to the probability that female mammals play important roles, even after copulation has begun, in determining whether their offspring will be sired by any given male (4, 5). This note urges that attempts be made to use this insight from animal studies to improve artilicial insemination techniques in humans. Substantial numbers of human couples arc childless against their will (6), and artificial insemination by donor (AID), a commonly used technique to overcome this problem, is frequently unsuccessful (7, 8). The most common techniques of AID in humans (9, 10) as well as in most domestic mammals (11) do not include attempts to make the stimuli associated with AID resemble those of natural copulations. There are two interesting exceptions. Artificial insemination in Dare received 15 February 1991 Date accepted 23 April 1991
152
mice commonly involves mating the female to a vascctomized male soon after sperm are introduced into her cervix or uterus, or simulating mating with a vaginal tampon (12). Stimuli associated with copulation in mice induce production of progesterone which elicits changes in the uterine lining facilitating implantation (13); numbers of females successfully impregnated by artifcial insemination were more than tripled, and litter sizes nearly doubled by use of an artificial penis and a vaginal tampon (14). Some AID in swine is performed with a pipette with a spiral tip similar to the tip of a boar’s penis; use of such pipettes usually results in less backflow of semen (1.5). In several other mammals stimulation of the female has been shown to increase the chances of reproduction. In rabbits, the number of artificially introduced sperm reaching the Fallopian tubes increased by a factor of four when artificial insemination was folllowed by copulation with a vasectomized male (16). Mechanical distension of the rabbit vagina produces uterine contractions that are probably important in sperm transport (4). In rats, preparation of the uterine lining for implantation and maintenance of the blastocyst is
ARTIACIAL
INSEMINATION
reliably induced by vaginal-cervical stimulation with probes and vibrators (17). The multiple intromissions whilch precede ejaculation in this species, as in some primates (18), promote transcervical sperm transport (19)~; the cumulative stimulatory effect of multiple intromissions can be stored (‘remembered’) by female rats for at least 4 h (20). Male golden hamsters add rcpctitivc intravaginal thrusts during long intromissions late in copulation scquenccs after sperm transfer has already occurred (21); these long intromissions are especially effective in initiating pregnancy, increasing pregnancy rates up to eight times over those resulting from some controls (22). As in other mammals such as goats (23), cattle (24.1, and horses (25). the male genitalia of humans perform complex movements and change form during ejaculation (26). It seems unlikely that such complex and consistent behavior is bereft of reproductive significance. ‘Superoptimal’ patterns of stimuli, which even more effectively increase the probability of the uterus becoming receptive to implantation than does normal male behavior under artiticial conditions, have been found in rats (27). Fertility can also bc affected by general surroundings during artificial insemination. For instance, pregnancy is less likely to result when AID in sheep is pcrfomtcd in the presence of distracting stimuli such as unfamiliar surroundings or barking dogs (28). Coinclusion
if
