Intrafollicular Pressure Research Articles

P-771 Does follicle size impact effect of follicular flushing on oocyte retrieval rate and embryology outcomes?

Abstract Study question Is the effect of follicular flushing on oocyte retrieval rate (RR) and embryology outcome influenced by follicular size? Summary answer Flushing improved RR in discordant growth with smaller(8-12 mm) follicles and larger(>22mm) follicle. Flushing did not impact embryological outcomes adversely. It increased top quality embryo What is known already Follicular flushing is done in poor responder for improving retrieval rate. There are very few studies in normal or hyper responders. Studies show controversial results of flushing, some showing benefits, while others, a detrimental effect because of increased intra-follicular pressure, increased procedure time, and change in paracrine milieu of oocytes by dilution with flushing medium No study has addressed whether increased retrieval rates with flushing are dependent on follicular size and indirectly maturity of oocyte. Most studies flushed with fixed volume of 1-2ml as size of follicle was not taken into account, making volume inadequate for completely flushing larger follicles. Study design, size, duration Prospective cohort study conducted from September 2022 to August 2023. Group 1: Study group- follicles were flushed after aspiration. Total patients were 120. They were divided into 3 groups according to follicular size and fluid volume aspirated with sample size calculated as A:306 small follicles 8-12 mm(<1.0ml), B:467 medium follicles 13-22 mm (1.0-6.0ml) C:102 large follicle > 22 mm (>6.0 ml). Group 2- Control group where follicles aspirated without flushing in 280 patients, 2572 follicles. Participants/materials, setting, methods Ethical approval taken. Inclusion - patients 21-40years of age undergoing oocyte retrieval for IVF/ICSI cycle with antagonist protocol Exclusion of oocyte of indeterminate origin ie one aspirate have two oocytes Group1 After aspiration of follicle with double lumen oocyte retrieval needle, follicle flushed with media volume equivalent to follicular volume. Group2 only follicular aspiration and volume measured Analysis done using SPSS-25 version. Primary outcome retrieval rate(RR) of oocytes. Secondary outcome: fertilization rate, percentage of top quality embryos(TQE)on day3&5, blastocyst rate. Main results and the role of chance Flushing follicle significantly increased RR in smaller follicles(8-12mm) compared to controls 159/311 (51.12%)vs 176/780 (22.56%) p = <0.001 and also in larger follicles(>6ml) 76/109 (69.72%)vs 116/219 (52.96%) p = <0.01 No difference seen in optimum size follicles (13-22mm) 337/470 (71.7%)vs 1099/1573(69.86%) p = 0.44. Overall, there was statistically significant increase in RR with flushing 567/890 (63.7%)vs 1391/2572 (54.08%) p = <0.001. Significantly more time was taken for flushing vs control groups 16.50vs 12.15 minutes p = <0.001. Secondary outcomes like fertilization rate was not different with flushing 476/567 (83.95±15.01%)vs 1125/1391(80.88±19.01 %) p = 0.21. Percentage of TQE (day 3) were significantly more in flushing group 321/476 (67.43±25.41%)vs control 642/1125 (57.07±25.94%)p = <0.01. TQE (day 5) were significantly more in flushing group 142/476 (29.83±11.02)vs control 251/1125 (22.31±12.11%)p=0.04. Blastocyst rate remained similar in both groups 196/476 (41.18±16.73 %) vs 403/1125 ( 35.82±13.90 %) p = 0.12. Subgroup analysis showed that younger women (<35yrs)had a significantly higher RR with flushing 66.33±16.29%vs controls 57.88±13.68% (p = <0.01), compared to older women >35 years 60.29±16.37%vs 56.35±17.30% (p = 0.38). Women with higher AMH had better RR with flushing 63.71±15.11%vs controls 56.50±14.33 (p = 0.01) compared to women with lower AMH (<1 ng/ml) where flushing made no difference 63.47±19.59%vs 60.62±14.93(p = 0.79). Normal and hyper responders had significantly higher RR with flushing 66.16±15.11vs controls 57.53±13.85%(p = <0.001) compared to poor responders (<5 oocytes) 51.07±18.07vs 56.24±27.47(p = 0.55). Limitations, reasons for caution Although RR was better with flushing in small and large follicles we could not translate the advantage to pregnancy rate(PR) PR could not be calculated as some patients wanted 2 embryos transferred. Since patient had one each embryos from small and optimum follicles both were transferred. Further RCT required. Wider implications of the findings Practice of follicular flushing needs re-evaluation Women with discordant growth should be taken for flushing as it increases RR in small and large follicles Role of flushing should be widened beyond poor responders to younger women, with normal or hyper response increasing oocyte yield which may increase cumulative pregnancy rate Trial registration number not applicable

The introduction of a double-channel system for the intrafollicular treatment of cattle

The aim of this study was to evaluate a new double-channel system for ultrasound-guided transvaginal intrafollicular treatment in cattle. The system is equipped with separate aspiration and treatment channels facilitating the aspiration of a small part of follicular fluid followed by the immediate injection of the same amount of treatment solution. In Experiment 1 an intracystic injection was performed successfully in all cows (6/6). In Experiment 2 saline was administered to dominant follicles with an overall success rate of 87.5% (14/16). This new double-channel system represents a reliable method for intrafollicular treatment preceded by an aspiration of the necessary amount of follicular fluid without an increase in intrafollicular pressure.  

Changes in intrafollicular pressure in the rat ovary by nitric oxide and by alteration of systemic blood pressure

Background: ovulation is associated with degradation of the follicular apex vasodilatation and increased permeability of ovarian vessels. These changes may maintain or increase intrafollicular pressure (IFP) at ovulation to cause rupture of the follicular wall. Objective: to investigate the possible regulation of IFP during the ovulatory process. Study design: immature Sprague–Dawley rats were primed with pregnant mare serum gonadotrophin (PMSG; 10 IU) and given hCG (10 IU) 48 h later. The ovary was exposed 48–60 h after PMSG, micropipette inserted into the Graafian follicle and the IFP measured at three time periods: preovulatory (PO) 48 h after PMSG; midovulatory (MO) 4–7 h after hCG; late ovulatory (LO) 9–12 h after hCG. The offset of the nitric oxide synthase (NOS) inhibitor l-arginine methyl ester ( l-NAME), the α 1-adrenoceptor agonist phenylephrine and the β-adrenoceptor agonist isoprenaline were tested. Results: phenylephrine given i.v. increased the systemic blood pressure, and significantly decreased the IFP in the LO phase (78% of pre-treatment value). Local administration of phenylephrine or isoprenaline (1 ml of 1.5–15 μM) by superfusion over the ovary did not change the IFP. Local administration of l-NAME (1 ml of 2 μM) significantly lowered ( P<0.05) the IFP in the MO and LO phases, but was without effect in the PO phase. Conclusion: this study reveals that IFP regulation may be related to changes of the systemic blood pressure and that NO may be one local ovarian mediator in IFP regulation.

Novel method for intrafollicular pressure measurements in the rat ovary: increased intrafollicular pressure after hCG stimulation

The ovulatory process in the rat comprises a period of about 12-15 h, from the time of the preovulatory LH surge to follicular rupture and extrusion of the oocyte. Follicular rupture is most likely caused, at least in part, by decreased tensile strength at the follicular apex due to degradation of collagen fibres of the extracellular matrix. It has been debated whether changes in intrafollicular pressure occur during the ovulatory process and whether such changes facilitate rupture of the follicle. In the present study, rats were primed with equine chorionic gonadotrophin (eCG, 10 iu) followed by hCG (10 iu) 48 h later. The intrafollicular pressure in the preovulatory follicle was recorded during 1 h at distinct time phases of the ovulatory process by use of an active servo-null pressure system based on the proportionality between electrical resistance and pressure within the tip of an inserted micropipette. The basal intrafollicular pressure was 16.6 +/- 1.0 mm Hg at the preovulatory phase (48 h after eCG) and increased gradually throughout the ovulatory process to 21.4 +/- 2.4 mm Hg at 4-7 h after hCG (mid-ovulatory phase) and 23.9 +/- 1.9 mm Hg at 8-12 h after hCG (late ovulatory phase; significantly higher (P < 0.01) than the preovulatory phase). Short-term peaks of increased pressure, possibly representing contractility, were not detected in follicles of the preovulatory phase, but were seen in most follicles of the mid- and late ovulatory phases. The mean amplitude of the short-term pressure increases was 12.3 +/- 3.2 mm Hg and the increases occurred at intervals of 24.7 +/- 3.6 s. These short-term increments in intrafollicular pressure were still present after hysterectomy had been performed. The wall tension index was calculated by measuring the follicular size and estimating the thickness of the follicle wall. The index increased from 93.9 +/- 13.3 at the preovulatory phase to 207.3 +/- 47.7 (mid-ovulatory phase) and to significantly higher values at the late ovulatory phase (320.9 +/- 33.5). In conclusion, this study shows that there is an increase in intrafollicular pressure in the ovulating follicle of the rat ovary during the late stages of the ovulatory process, and that short-term increases in intrafollicular pressure occur during the late phase of the ovulatory process. These changes in pressure may be essential for follicular rupture to proceed normally.

Novel method for intrafollicular pressure measurements in the rat ovary: increased intrafollicular pressure after hCG stimulation.

The ovulatory process in the rat comprises a period of about 12-15 h, from the time of the preovulatory LH surge to follicular rupture and extrusion of the oocyte. Follicular rupture is most likely caused, at least in part, by decreased tensile strength at the follicular apex due to degradation of collagen fibres of the extracellular matrix. It has been debated whether changes in intrafollicular pressure occur during the ovulatory process and whether such changes facilitate rupture of the follicle. In the present study, rats were primed with equine chorionic gonadotrophin (eCG, 10 iu) followed by hCG (10 iu) 48 h later. The intrafollicular pressure in the preovulatory follicle was recorded during 1 h at distinct time phases of the ovulatory process by use of an active servo-null pressure system based on the proportionality between electrical resistance and pressure within the tip of an inserted micropipette. The basal intrafollicular pressure was 16.6 +/- 1.0 mm Hg at the preovulatory phase (48 h after eCG) and increased gradually throughout the ovulatory process to 21.4 +/- 2.4 mm Hg at 4-7 h after hCG (mid-ovulatory phase) and 23.9 +/- 1.9 mm Hg at 8-12 h after hCG (late ovulatory phase; significantly higher (P < 0.01) than the preovulatory phase). Short-term peaks of increased pressure, possibly representing contractility, were not detected in follicles of the preovulatory phase, but were seen in most follicles of the mid- and late ovulatory phases. The mean amplitude of the short-term pressure increases was 12.3 +/- 3.2 mm Hg and the increases occurred at intervals of 24.7 +/- 3.6 s. These short-term increments in intrafollicular pressure were still present after hysterectomy had been performed. The wall tension index was calculated by measuring the follicular size and estimating the thickness of the follicle wall. The index increased from 93.9 +/- 13.3 at the preovulatory phase to 207.3 +/- 47.7 (mid-ovulatory phase) and to significantly higher values at the late ovulatory phase (320.9 +/- 33.5). In conclusion, this study shows that there is an increase in intrafollicular pressure in the ovulating follicle of the rat ovary during the late stages of the ovulatory process, and that short-term increases in intrafollicular pressure occur during the late phase of the ovulatory process. These changes in pressure may be essential for follicular rupture to proceed normally.

Current Status of the Hypothesis that Mammalian Ovulation is Comparable to an Inflammatory Reaction

This presentation reviews current information on the events that lead to rupture of an ovarian follicle. It contains a summary of the morphological changes that occur at the apex of a follicle wall during ovulation. Existing information shows that the tenacious connective tissue layers of the tunica albuginea and theca externa must be weakened before the follicle wall can dissociate and break open under the force of a modest intrafollicular pressure. These changes are probably dependent on transformation of quiescent thecal fibroblasts into proliferating cells in a manner that is characteristic of tissue responses to inflammatory reactions. The metabolic factors that initiate transformation of the fibroblasts are uncertain, but they are probably generated by gonadotropin-induced changes in the theca interna and granulosa of a follicle as these layers begin to luteinize during the ovulatory process.

In vitro study of the contractility of the wall of the preovulatory follicle in the Japanese quail.

In the present study, we examined in vitro the potassium-induced contractions of isolated parts of the wall of the quail preovulatory follicle through use of an electromagnetic force-length transducer system. We studied longitudinal and transverse strips of the whole wall, of the theca, and of the outer layer (tunica albuginea and surface epithelium). It was observed that force development and shortening of strips of the whole wall and those of the theca are similar. Statistical analysis of maximal isometric force, peak shortening length, and percentage of reduction of follicular volume showed that the orientation of strips is without importance. Results from different orientations were pooled, and the different layers were compared statistically. The general result of this analysis was that the contractile activity of the outer layer was significantly lower than the performance of either the whole wall or the theca. We concluded that contraction of the follicular wall is mainly dependent on the contractile activity of the theca externa. This contractile system is comparable to that of mammals. We suggest that the main function of the theca externa during ovulation is to maintain a constant intrafollicular pressure.

Physicochemical properties of follicular fluid and their relation to in vitro fertilization (IVF) outcome

Despite the limited data that are available concerning FF physicochemical properties, the following conclusions can be drawn. (1) FF temperature is lower than ovarian stroma and body temperatures. The physiological significance of this gradient is unknown. (2) Follicular size increases exponentially prior to ovulation. The relationship between FF volume and successful IVF outcome is well established. (3) A highly significant association exists between fertilization (but not embryo cleavage) and FF spectrophotometric absorbance at delta optic density of 455 nm. (4) FF behaves as a non-Newtonian fluid--its viscosity changes at different shear rates. Neither FF viscosity nor its refractive index was found to correlate with the presence of oocytes, their maturation grade, or their fertilizing capacity. (5) FF osmolarity is similar to that of the plasma. There is no information linking variations in FF osmolarity to IVF outcome. (6) FF pH is acidic, probably due to acid mucopolysaccharides. It appears that the intact follicle is capable of buffering any carbon dioxide which diffuses through its wall at the time of intraperitoneal insufflation. The transvaginal aspiration technique eliminates any possible effect of exogenous gas on FF pH. (7) Regarding the intact follicle, it was shown that (a) there is a small potential difference across the follicle wall, and (b) intrafollicular pressure remains steady prior to ovulation. This information may shed some light on mechanisms underlying FF formation and ovulation. No experiments relating these properties to IVF outcome have been performed.

Relaxation-induced contraction of smooth muscle surrounding hamster ovarian follicles.

Changes in intrafollicular pressure and follicular diameter resulting from injecting or withdrawing fluid from the antrum were measured in preovulatory follicles and used as an assay for changes in tension in the follicular wall by applying the Laplace relationship for thin-walled spheres. Passive length-tension curves were constructed from pressure-volume measurements to establish baseline wall stiffness. Any subsequent change in pressure could then be compared to the length-tension curves to evaluate whether it arose from active tension development or from passive stretch. When intact follicles (1-2h before ovulation) were subjected to release of passive stretch, they exhibited a contractile response that lasted 15 sec-2 min and was characterized by cyclic increases and decreases in tension, with a period of 1 cycle every 2-3 sec. The probability of activating a response in the tissue was most strongly correlated with the rate of release of passive stretch. Intrafollicular pressures generated during active contractile responses sometimes reached 80 mmHg (10.64 mPa), corresponding to a wall tension of 5332 dynes/cm (5.332 N/m) (for a 1 mm follicle) and were clearly well above the passive length-tension curves. Passive stretching of the follicular wall during a contractile response to 5-hydroxytryptamine stimulation resulted in large reductions in active wall tension for the duration of the stretch. These results are consistent with a stretch-activated inhibition of contractile events.

Intrafollicular pressure promotes partial evacuation of the antrum during hamster ovulation in vitro

AbstractThe role of intrafollicular pressure in evacuation of the hamster cumulus from the follicle at ovulation was investigated experimentally in vitro. Previous work has shown that the cumulus is generally evacuated in two stages (Talbot, '82). Phase 1 occurs immediately at rupture and is characterized by rapid (&lt;60 seconds) extrusion of about 20% of the cumulus and usually the oocyte. Phase 2 includes the gradual (2–10 minutes) removal of the remainder of the cumulus and collapse of the follicle wall. Fresh or aged follicles (approximate intrafollicular pressures = 2.1 or 0.0 mmHg, respectively) were poked with “0” gauge insect pins to produce a rupture site in their apices. Of 69 fresh follicles tested, 68 responded with phase 1 extrusion; 57 of the 68 evacuated the oocyte in addition to a significant portion of the cumulus. In contrast, only seven out of 80 aged follicles showed phase 1 extrusion, and only three out of these seven extruded the oocyte. To verify that phase 1 extrusion in fresh follicles was due to intrafollicular pressure and not smooth muscle cell (SMC) contraction, some fresh poked follicles were fixed for microscopy. Twelve of 14 follicles had flat bases or small V‐shaped constriction in their bases, indicating SMC contraction had not occurred. This was further substantiated by examining several follicles with transmission electron microscopy; SMC in the theca externa were relaxed by morphological criteria. To determine if phase 2 extrusion occurred in poked follicles, fresh follicles were poked, cultured in vitro for 3 hours, and examined microscopically. Phase 1 occurred in all follicles after poking. The remainder of the cumulus was eventually evacuated from the antrum, although much more slowly than during normal in vitro ovulation. The follicle wall did not collapse in these trials. We conclude that intrafollicular pressure is responsible for phase 1 extrusion, i.e., rapid passage of part of the cumulus and oocyte through the rupture site, and that intrafollicular pressure will promote phase 1 extrusion in the absence of SMC contraction. The remainder of the cumulus can be evacuated in the absence of IFP and collapse of the follicle wall; perhaps this occurs by hydration of that portion of the cumulus evacuated during phase 1. Hydration would tend to expand the cumulus and pull the remaining cumulus from the antrum. These results establish a role for intrafollicular pressure in hamster ovulation.

Intrafollicular pressure decreases in hamster preovulatory follicles during smooth muscle cell contraction in vitro.

Smooth muscle cells in the base of hamster follicles contract minutes prior to ovulation; during this contraction the profile of the follicle changes from low to tall. Our purpose was to measure intrafollicular pressure, independent of an intact circulatory system to the ovary, at the time when follicular smooth muscles are known to be contracting. Hamster ovaries were removed 13 hours after hCG injection and placed in a culture medium which supports in vitro ovulation. Intrafollicular pressure was measured continuously with a WPI Model 900 Micropressure system, while the follicle was being observed and photographed using a dissecting microscope and Zeiss 35 mm camera. Initial intrafollicular pressure was 2.1 +/- 1.1 mmHg (n = 47) in the absence of a blood supply. This pressure decreased slowly (0.03 mmHg/min.) until the transition from a low to tall profile occurred at which time the pressure decreased at a rate of 0.09 mmHg/min. At ovulation, the pressure drops precipitously to 0.0 mmHg. The condition of the follicle, in particular the apex, was examined using scanning electron microscopy (SEM). At 13 hours after hCG, rupture sites had started forming in the apices of 94.3% of the unovulated follicles. In some instances, surface epithelial cells were stretched apart and gaps were present between cells. More often portions of the surface epithelium were missing and the underlying cell layers were exposed. Fluid and erythrocytes were observed passing through the developing rupture sites. Taken together these observations demonstrate that intrafollicular pressure in hamster preovulatory follicles decreases gradually at the time follicular smooth muscle cells contract. We suggest that contraction of follicular SMC is a slow, gradual process which causes formation and/or enlargement of holes in the rupture site. An increase in the size or number of these apertures would lead to increased leakiness and could account for the observed acceleration in the rate of pressure decrease during profile transition. Our observations are the first to correlate changes in intrafollicular pressure with the contraction of smooth muscle cells and condition of the apex.

5-Hydroxytryptamine causes contraction of smooth muscle cells in preovulatory hamster follicles.

AbstractWe have examined the effect of 5‐hydroxytryptamine (5‐HT) on ovaries removed from hamsters and placed in culture 12 or 13 hours after hCG injection. The four responses to 5‐HT which were studied include: (1) contraction of follicular smooth muscle cells (SMC), (2) formation of a V‐shaped constriction in the base of follicles, (3) changes in the profile of follicles, and (4) changes in intrafollicular pressure. Our results show that 10−3 M 5‐HT alters the ultrastructure of follicular SMC to that characteristic of a contracted state. The contraction of these SMCs produces in turn: (1) a V‐shaped constriction in the base of the follicle similar to that observed in unstimulated 13 hour ovaries undergoing in vitro ovulation (Martin and Talbot, '81a), and (2) a change in the profile of the follicle which becomes taller and more spherical, but not identical to the “true” tall follicle seen during normal in vitro ovulation. The fact that 5‐HT does not change the follicle to a “true” tall profile and does not induce immediate ovulation in most cases (even though SMC are contracted) suggests to us that the apices of these follicles were not sufficiently weakened by enzymes to permit immediate rupture when SMC contracted. The response of SMC to 5‐HT was immediate, rapid, sustained at least 10 minutes, and could be inhibited by methysergide. The latter observation suggests that 5‐HT interacts with “D” receptors of SMC and not “M” receptors of nervous tissue. The degree of contraction elicited by 5‐HT varied from one follicle to another; many SMC did not appear maximally contracted by morphological criteria. Intrafollicular pressure increased in most follicles treated with 5‐HT; pressure returned to initial levels relatively quickly, presumably because fluid was able to seep through developing ruptures in the apex. Intrafollicular pressure does not increase during unstimulated in vitro ovulation (Schroeder and Talbot '82). We interpret the intrafollicular pressure data of this study to mean that 5‐HT elicits a much more rapid contraction of SMC than would ordinarily occur in vitro. Thus, SMC contraction in follicles not stimulated by 5‐HT would be a slow, gradual, process allowing constant or decreasing levels of pressure to be maintained. Our observations are important in directly showing that: (1) 5‐HT stimulates contraction of SMCs in hamster follicles, and (2) this contraction produces a V‐shaped constriction in the base of the follicle and a change in the profile of the follicle, and (3) that intrafollicular pressure will increase abruptly upon strong, simultaneous contraction of follicular SMC. These observations provide further support for our earlier statement that SMC function in hamster ovulation (Martin and Talbot,'81a).

Intrafollicular Pressure within Preovulatory Follicles of the Pig

Antral pressure was measured within the follicles of unstimulated ovaries in prepubertal pigs and following an ovulatory stimulus with exogenous gonadotropins. No increase in intrafollicular pressure (IFP) was observed as the time of ovulation approached. A wide range of IFP was noted within follicles of the unstimulated ovary. In many follicles IFP was greater than 30 cm H2O, suggesting that the antral fluid was not in hydrostatic equilibrium with the surrounding thecal capillaries. IFP of unstimulated follicles could be increased to more than 400 cm H2O by antral injection of mineral oil without follicular rupture--a demonstration of the need for stigma formation in the release of the ovum from the follicle. Stimulated follicles were found to be more distensible than unstimulated follicles. The follicles also fell into two groups--those in which sustained versus transient elevation in IFP occurred following oil injection. It is postulated that the follicle wall develops the ability to undergo stress relaxation during follicular maturation and that this process plays a role in regulating IFP.

Studies on the dependence of intrafollicular pressure on the pressure in the intraovarian-vascular-system and tissue, carried out in vitro on human ovaries (author's transl)

The intrafollicular, intraovarian and intraarterial hydrostatic pressures were measured in vitro on human ovaries in the vollicular ripening phase. It has been established that in the vascular system as well as in the intraovarian tissues pressure variations occur spontaneously. Thus for example under, the influence of epinephrine, norepinephrine, prostaglandine F2 alpha and oxytocine, the tonicity of the vascular system increases and does so the number of spontaneous contractions rather noticeably, particularly under the influence of prostaglandine F2alpha, and under the various catecholamines an increase of frequency and amplitude has been observed. Any increase of pressure in the intraovarian vascular system and tissues will effect all the follicles not yet in the preovulatorian phase, in which they cause a similar pressure increase. However, follicles imminently preovulatorian have not shown such pressure increase because the increase of the "liquor folliculi" runs parallel to the increasing elasticity of the follicle walls. The findings are discussed in this article with a particular view of the biophysical aspects of ovulation.

Induction of ovulation in human ovaries perfused in vitro.

An in vitro ovulation could be induced and observed in four human ovaries with Graafian follicle. Perfusion was carried out by means of a semi-synthetic medium which was free from haemoglobin in a closed recirculating system. During the stimulation by means of HCG/HMG (after the II. IRP a total of 22.9 I.U. LH/ml and 3 I.U. FSH/ml) an activation of respiration and glycolysis by a factor of 2–3up to the rupture of the follicle was observed. In this process 93% of the energy were released by the oxydative reduction of glucose and only about 7% by anaerobic glycolysis. 60–90 minutes before the rupture of the follicle an undulatory rise in the arterial hydrostatic pressure of up to 40 mmHg over the initial values was observed, although the outward conditions of perfusion were not altered, after the rupture a pressure drop to standard values. Apart from minor oscillations there was no increase in the intrafollicular pressure in spite of an increase in volume of the follicle, but only a decrease in pressure after the rupture of the follicle.

Spontaneous contractions of the human ovary in vitro.

The mechanism controlling the last step in ovulation—ejection of the follicular contents—is not yet fully explained. Several hypotheses have been proposed, for example, increased intrafollicular pressure (Bartelmez, 1912; Smith, 1934; Jensen & Zacharia, 1960), contractions of the follicular wall (Lipner & Maxwell, 1960), and enzymatic breakdown (digestion) of the follicular wall (Espey & Lipner, 1965; Espey, 1967; Espey, Slagter, Weymouth & Rondell, 1965; Espey & Rondell, 1968; Rondell, 1970) but none has been proven to be the mechanism of ovulation. However, it is agreed by all that a fully developed stigma is essential for ovulation. Recently, spontaneous contractions of cat ovaries in vitro were demonstrated and a response to adrenergic drugs was shown (Rocereto, Jacobowitz & Wallach, 1969). These contractions were assumed to be under the control of sympathetic impulses mediated through the adrenergic innervation (Jacobowitz & Wallach, 1967; Rocereto et al., 1969) to the smooth muscle cells found in

Biophysical Aspects of Ovulation

The author arrives at a hypothesis for ovarian processes in ovulation through examination of his own work and that of others in the field of ovarian ovulatory mechanisms. The mechanical aspects of follicular rupture are the main points considered. It appears that no significant change in intrafollicular pressure occurs in ovulation. On the other hand, a marked increase in wall tissue distensibility occurs and is probably associated with a decrease in breaking strength. A relatively small change in distensibility could produce an unstable follicle which would rupture with normal intrafollicular pressures. The collagen component is probably important to the wall's structural strength. In ovulation the interfibrillar bonding may be interfered with so that tension upon stretching is reduced and increased slippage of fibrils past one another occurs. Though a collagenase-like enzyme has been identified in the follicular tissue and appears to be released at ovulation, no definite link has been made between this enzyme and the increase of follicular distensibility in vivo. If luteinizing hormone stimulates the synthesis or release of an ovulatory enzyme, it probably does so by stimulation or steroid secretion rather than by direct stimulation of enzyme synthesis or release. With more knowledge, fertility control may be achieved at the level of the ovary without simultaneous control though trophic factors.

The Effect of Feather Muscle Receptor Stimulation on Intrafollicular Pressure, Feather Shaft Movement and Feather Release in the Chicken ,

INTRODUCTIONOSTMANN et al. (1963) found that feathers were loosened by both local and general anesthetics by tranquilizing drugs such as chlorpromazine and promazine and by the neural blocking drugs atropine and yohimbine. On the other hand, adrenergic and cholinergic drugs had no effect on altering feather pulling force. In addition, Ostmann et al. (1964) observed that all levels of spinal transaction significantly reduced feather pulling force posterior to the level of transection.The present investigation was undertaken to determine if the feather muscles have adrenergic (alpha and/or beta) and cholinergic receptors. In addition to the above, the effects of feather muscle receptor stimulation on intrafollicular pressure, feather release and feather shaft movement were also studied.METHODSThe pressure within the feather follicle (intrafollicular pressure or IFP) was measured using a technique developed by Peterson and Ringer (1964). Non-molting mature S. C. White Leghorn-type hens were used throughout the experiments. .

FOLLICULAR PRESSURE AND DISTENSIBILITY IN OVULATION

Micropipettes were introduced into follicles of exteriorized ovaries of rabbits anesthetized with pentobarbital. One pipette served for measurement of hydrostatic pressures, a second for the injection of small, measured amounts of saline. Impending ovulation did not measurably influence intrafollicular hydrostatic pressure. Artificial rupture could not be induced by increasing intrafollicular pressure by the injection of fluid. Tension-length diagrams for the elastic elements of the follicular wall, constructed from pressure measurements made following intrafollicular injections, indicate that a large increase in extensibility precedes rupture. Such a change in the physical characteristics of the follicle wall appears to be an essential part of the mechanism of ovulation.

Intrafollicular Pressure in the Feather Follicle ,

A PREVIOUS report by Ostmann, Ringer and Tetzlaff (1963) indicated that anesthetics, sympathetic and parasympathetic blocking agents, and tranquilizing drugs caused the feather to loosen within its follicle. These workers did not clarify the exact role played by the muscles and wall of the feather follicle in feather release.An experiment using intrafollicular pressure as a measurement was designed to study the mechanism involved in the loose and tight states within the feather follicle. EXPERIMENTAL PROCEDUREMature S. C. White Leghorn hens were secured on an operating cradle which held them virtually motionless. A mature feather was randomly selected for studying intrafollicular pressure from either the femoral or caudal feather tract. With procaine used as a local anesthetic, one of the brachial veins was then cannulated for the subsequent injection of sodium pentobarbital.All feather shafts in the immediate area of the chosen feather were cut at the level of…